diff --git a/ChatController/ChatController.csproj b/ChatController/ChatController.csproj
index 29222fe..89e43ea 100644
--- a/ChatController/ChatController.csproj
+++ b/ChatController/ChatController.csproj
@@ -149,6 +149,7 @@
   </ItemGroup>
   <ItemGroup>
     <Content Include="ownchat_favicon.ico" />
+    <Resource Include="Ressourcen\warning-exclamation-mark.png" />
     <None Include="packages.config" />
     <None Include="Resources\oC-favico_NewMessage.ico" />
     <Content Include="Resources\ownchat_favicon.ico" />
diff --git a/ChatController/ChatMainControl.xaml b/ChatController/ChatMainControl.xaml
index e36002d..a85ed94 100644
--- a/ChatController/ChatMainControl.xaml
+++ b/ChatController/ChatMainControl.xaml
@@ -66,6 +66,7 @@
             <Setter Property="Template" Value="{StaticResource ContactListBoxTemplate}" />
         </Style>
 
+        <!-- Kontaktliste -->
         <Style x:Key="ContactListBoxItemStyle" TargetType="{x:Type ListBoxItem}">
             <Setter Property="HorizontalContentAlignment" Value="{Binding Path=HorizontalContentAlignment, RelativeSource={RelativeSource AncestorLevel=1, AncestorType={x:Type ItemsControl}, Mode=FindAncestor}}" />
             <Setter Property="VerticalContentAlignment" Value="{Binding Path=VerticalContentAlignment, RelativeSource={RelativeSource AncestorLevel=1, AncestorType={x:Type ItemsControl}, Mode=FindAncestor}}" />
@@ -210,29 +211,20 @@
                         <RowDefinition Height="Auto"/>
                     </Grid.RowDefinitions>
 
-                    <ListBox x:Name="AktChatUserList"  HorizontalAlignment="Left" Margin="0" Grid.Row="0" Background="Transparent"  BorderBrush="Transparent" VerticalAlignment="Bottom"  ItemTemplate="{DynamicResource DataTemplate2}" MouseDoubleClick="AktChatUser_OnMouseDoubleClick" >
-                        <ListBox.Resources>
-                            <DataTemplate x:Key="DataTemplate2" DataType="chatKlassen:Contact">
-                                <Grid>
-                                    <Grid.ColumnDefinitions>
-                                        <ColumnDefinition Width="50"/>
-                                        <ColumnDefinition Width="*"/>
-                                    </Grid.ColumnDefinitions>
-                                    <Grid.RowDefinitions>
-                                        <RowDefinition Height="10*" />
-                                    </Grid.RowDefinitions>
+                    <Grid Grid.Row="0" HorizontalAlignment="Left" Background="Transparent" VerticalAlignment="Center" Height="50" PreviewMouseDown="CurrentContactImage_OnMouseDoubleClick">
+                        <Grid.ColumnDefinitions>
+                            <ColumnDefinition Width="50" />
+                            <ColumnDefinition Width="*" />
+                        </Grid.ColumnDefinitions>
 
-                                    <Ellipse Width='40' Height='40' VerticalAlignment="Center" RenderOptions.BitmapScalingMode="HighQuality">
-                                        <Ellipse.Fill >
-                                            <ImageBrush ImageSource='{Binding Image}' Stretch="UniformToFill"/>
-                                        </Ellipse.Fill>
-                                    </Ellipse>
-
-                                    <TextBlock Grid.Column="1" Margin="8" Text="{Binding Path=Name, FallbackValue=FirstName}" FontSize="16" Foreground="{Binding AccentColorBrush}" />
-                                </Grid>
-                            </DataTemplate>
-                        </ListBox.Resources>
-                    </ListBox>
+                        <Ellipse Width='40' Height='40' VerticalAlignment="Center" RenderOptions.BitmapScalingMode="HighQuality">
+                            <Ellipse.Fill >
+                                <ImageBrush ImageSource='{Binding Path=ThreadExceptionImageSource, UpdateSourceTrigger=PropertyChanged}' Stretch="UniformToFill"/>
+                            </Ellipse.Fill>
+                        </Ellipse>
+                        
+                        <TextBlock Grid.Column="1" VerticalAlignment="Center" Margin="8" TextWrapping="Wrap" Text="{Binding CurrentContactInformationString}" FontSize="16" Foreground="{Binding CurrencContactInfoForeground}" />
+                    </Grid>
 
                     <ListBox x:Name="ChatListBox" ItemsSource="{Binding CurrentChatMessages, UpdateSourceTrigger=PropertyChanged}"
                              HorizontalAlignment="Stretch"  ScrollViewer.CanContentScroll="False" VerticalAlignment="Stretch" Grid.Row="1" 
@@ -366,7 +358,8 @@
                                  Margin="2"
                                  VerticalAlignment="Stretch" 
                                  GotFocus="Chatbox_OnGotFocus" 
-                                 KeyDown="Chatbox_OnKeyDownHandler">
+                                 KeyDown="Chatbox_OnKeyDownHandler"
+                                 TextChanged="Chatbox_OnTextChanged">
                             <TextBox.Resources>
                                 <Style TargetType="{x:Type Border}">
                                     <Setter Property="CornerRadius" Value="2"/>
diff --git a/ChatController/ChatMainControl.xaml.cs b/ChatController/ChatMainControl.xaml.cs
index 69b92b1..f4719ce 100644
--- a/ChatController/ChatMainControl.xaml.cs
+++ b/ChatController/ChatMainControl.xaml.cs
@@ -14,6 +14,7 @@ using System.Windows.Data;
 using System.Windows.Forms;
 using System.Windows.Input;
 using System.Windows.Media;
+using System.Windows.Media.Imaging;
 using System.Windows.Navigation;
 using System.Windows.Threading;
 using ChatController.Annotations;
@@ -43,6 +44,33 @@ namespace ChatController
 
         private readonly Dictionary<int, SyncFileInfoStruct> _GroupId2DateTime = new Dictionary<int, SyncFileInfoStruct>();
 
+        private string _ThreadExceptionMessage;
+
+        public string ThreadExceptionMessage
+        {
+            get => _ThreadExceptionMessage;
+
+            set
+            {
+                if(!Equals(_ThreadExceptionMessage, value))
+                {
+                    _ThreadExceptionMessage = value;
+                    OnPropertyChanged(nameof(ThreadExceptionMessage));
+                    OnPropertyChanged(nameof(CurrentContactInformationString));
+                    OnPropertyChanged(nameof(CurrencContactInfoForeground));
+                    OnPropertyChanged(nameof(ThreadExceptionImageSource));
+                }
+            }
+        }
+
+        private readonly ImageSource _ThreadExceptionImageSource;
+
+        public ImageSource ThreadExceptionImageSource => ThreadExceptionMessage != null ? _ThreadExceptionImageSource : CurrentContact?.Image;
+
+        public SolidColorBrush CurrencContactInfoForeground => ThreadExceptionMessage != null ? new SolidColorBrush(Color.FromRgb(185, 65, 0)) : CurrentContact?.AccentColorBrush ?? new SolidColorBrush(Colors.Transparent);
+
+        public string CurrentContactInformationString => ThreadExceptionMessage ?? CurrentContact?.Name;
+
         private Window _ContainingWindow;
 
         public Window ContainingWindow
@@ -79,6 +107,9 @@ namespace ChatController
                     OnPropertyChanged(nameof(CurrentContact));
                     OnPropertyChanged(nameof(ChatMessageInputGridVisibility));
                     OnPropertyChanged(nameof(CurrentChatMessages));
+                    OnPropertyChanged(nameof(CurrentContactInformationString));
+                    OnPropertyChanged(nameof(CurrencContactInfoForeground));
+                    OnPropertyChanged(nameof(ThreadExceptionImageSource));
                 }
             }
         }
@@ -121,6 +152,8 @@ namespace ChatController
         public ChatMainControl()
         {
             InitializeComponent();
+            
+            _ThreadExceptionImageSource = new BitmapImage(new Uri("pack://application:,,,/ChatController;component/Ressourcen/warning-exclamation-mark.png", UriKind.Absolute));
 
             DataContext = this;
 
@@ -140,11 +173,24 @@ namespace ChatController
         public void InitMitChatdaten(ChatDatenUebergabe cdu)
         {
             _Chat = new Chat(cdu, exception => {
-                this.Dispatch(() => {
-                    EndWaiting();
-                    MessageBox.Show($"Fehler: {exception.Message}", "Fehler", MessageBoxButton.OK, MessageBoxImage.Error);
+                    this.Dispatch(
+                        () => {
+                            EndWaiting();
+
+                            MessageBox.Show($"Fehler: {exception.Message}", "Fehler", MessageBoxButton.OK, MessageBoxImage.Error);
+                        });
+                },
+                exception => {
+                    this.Dispatch(
+                        () => {
+                            if(exception == null)
+                            {
+                                ThreadExceptionMessage = null;
+                            }
+
+                            ThreadExceptionMessage = exception?.Message?.Contains("500") ?? false ? "ownChat ist vorrübergehend nicht verfügbar. Bitte versuchen Sie es später noch einmal." : null;
+                        });
                 });
-            });
 
             _ContactList = _Chat.AddContacts();
             OnPropertyChanged(nameof(ContactList));
@@ -235,10 +281,13 @@ namespace ChatController
             ReloadGruppen.Visibility = Visibility.Visible;
             _IsDesktopVersion = false;
         }
-        
-        private void AktChatUser_OnMouseDoubleClick(object sender, MouseButtonEventArgs e)
+
+        private void CurrentContactImage_OnMouseDoubleClick(object sender, MouseButtonEventArgs e)
         {
-            _Chat.ShowProfilePicture(_CurrentContact);
+            if(e.ClickCount == 2)
+            {
+                _Chat.ShowProfilePicture(_CurrentContact);
+            }
         }
 
         private void Clientlist_OnSelectionChanged(object sender, SelectionChangedEventArgs e)
@@ -262,8 +311,6 @@ namespace ChatController
             Cursor = Cursors.Wait;
             _ScrollPrueferAktivieren = false;
 
-            AktChatUserList.Items.Clear();
-
             if (pContact.HasUnreadMessages)
             {
                 pContact.HasUnreadMessages = false;
@@ -280,7 +327,6 @@ namespace ChatController
                 ContainingWindow.Icon = Utils.GetImageSourceFromIcon(Resource.ownchat_favicon);
             }
 
-            AktChatUserList.Items.Add(currentContact);
             CurrentContact = currentContact;
 
             if(Clientlist.Items.Contains(pContact))
@@ -368,8 +414,7 @@ namespace ChatController
 
         private void PasteOnClick(object sender, RoutedEventArgs routedEventArgs)
         {
-            var kontakt = (Contact)AktChatUserList.Items[0];
-            _Chat.Paste(kontakt.GroupId,this);          
+            _Chat.Paste(CurrentContact.GroupId,this);          
         }
 
         private void CopyOnClick(object sender, RoutedEventArgs routedEventArgs)
@@ -468,9 +513,8 @@ namespace ChatController
                     ContextItemSpeichernUnter.Visibility = Visibility.Collapsed;
                 }
 
-                //prüfe ob dokumentation erlaubt
-                var kontakt = (Contact)AktChatUserList.Items[0];
-                if(kontakt.UserIdManage == null && ChatListBox.ContextMenu.Items.Count > 3)
+                // Prüfe, ob Dokumentation erlaubt
+                if(CurrentContact.UserIdManage == null && ChatListBox.ContextMenu.Items.Count > 3)
                 {
                     var contextItems = ChatListBox.ContextMenu.Items;
                     var ContextItemSpeichernUnter = (MenuItem)contextItems[3];
@@ -492,7 +536,7 @@ namespace ChatController
 
         private void MediaButton_OnClick(object sender, RoutedEventArgs e)
         {
-            if (AktChatUserList.Items.Count > 0)
+            if(CurrentContact != null)
             {
                 var fileToOpen = _Chat.OpenFile();
 
@@ -510,7 +554,7 @@ namespace ChatController
 
                     if (!string.IsNullOrWhiteSpace(filePath))
                     {
-                        //_Chat.AddNewFile(filePath, fileToOpen, CurrentContact.GroupId);
+                        _Chat.AddNewFile(filePath, fileToOpen, CurrentContact.GroupId);
 
                         OnPropertyChanged(nameof(CurrentChatMessages));
                         
@@ -534,7 +578,7 @@ namespace ChatController
 
         private void SendButton_OnClick(object sender, RoutedEventArgs e)
         {
-            if (!AktChatUserList.Items.IsEmpty && !string.IsNullOrEmpty(Chatbox.Text))
+            if(CurrentContact != null && !string.IsNullOrEmpty(Chatbox.Text))
             {
                 _Chat.AddNewMessage(Chatbox.Text, CurrentContact.GroupId);
 
@@ -564,7 +608,7 @@ namespace ChatController
             {
                 if (e.Key == Key.Return)
                 {
-                    if (!AktChatUserList.Items.IsEmpty && !string.IsNullOrEmpty(Chatbox.Text))
+                    if(CurrentContact != null && !string.IsNullOrEmpty(Chatbox.Text))
                     {
                         _Chat.AddNewMessage(Chatbox.Text, CurrentContact.GroupId);
 
@@ -646,7 +690,7 @@ namespace ChatController
         {
             EmojisListeningThreadTimer?.Stop();
             EmojisListeningThreadTimer = null;
-            InitListeningThread((Contact)AktChatUserList.Items[0]);
+            InitListeningThread(CurrentContact);
         }
 
         public Timer EmojisListeningThreadTimer;
@@ -656,7 +700,7 @@ namespace ChatController
         {
             GlobalListeningThreadtimer = new Timer();
             GlobalListeningThreadtimer.Tick += GlobalListeningThreadTimerTickEvent;
-            GlobalListeningThreadtimer.Interval = 2000;
+            GlobalListeningThreadtimer.Interval = 10000;
             GlobalListeningThreadtimer.Start();
         }
 
@@ -677,13 +721,6 @@ namespace ChatController
                 {
                     var contacts = _Chat.NeueGroupklassenKontakte().ToList();
 
-                    Contact currentContact = null;
-
-                    if (AktChatUserList.HasItems)
-                    {
-                        currentContact = (Contact) AktChatUserList.Items[0];
-                    }
-
                     foreach (var contact in _ContactList)
                     {
                         foreach (var newContact in contacts)
@@ -696,15 +733,17 @@ namespace ChatController
                                     contact.ReceivedMessage = newContact.ReceivedMessage;
                                     contact.TimeStamp = newContact.TimeStamp;
 
-                                    // TODO: Prüfen, ob die App im Hintergrund oder minimiert ist
-                                    if (Clientlist.SelectedItem != null && !((Contact)Clientlist.SelectedItem).GroupId.Equals(newContact.GroupId) || Clientlist.SelectedItem == null || _IsInBackground)
+                                    var selectedContact = (Contact) Clientlist.SelectedItem;
+                                    var userOid = _Chat.ChatDaten.LoggedInUser.Response.User.Oid;
+
+                                    if (selectedContact != null && !selectedContact.GroupId.Equals(newContact.GroupId) || selectedContact == null || _IsInBackground && userOid != contact?.ReceivedMessage?.UserId)
                                     {
                                         ContainingWindow.Icon = Utils.GetImageSourceFromIcon(Resource.oC_favico_NewMessage);
                                         ShowNotification(newContact.Name, newContact.ReceivedMessage, newContact.GroupId);
                                     }
 
                                     // Wenn der momentan ausgewählte Kontakt der aktuelle Kontakt in der Schleife ist, werden die Nachrichten nicht als ungelesen angezeigt, sonst schon.
-                                    if (currentContact != null && newContact.GroupId == currentContact.GroupId)
+                                    if (CurrentContact != null && newContact.GroupId == CurrentContact.GroupId)
                                     {
                                         contact.HasUnreadMessages = false;
                                     }
@@ -737,7 +776,7 @@ namespace ChatController
         {
             EmojisListeningThreadTimer = new Timer {Tag = currentContact};
             EmojisListeningThreadTimer.Tick += ListeningThreadTimerTickEvent;
-            EmojisListeningThreadTimer.Interval = 2000;
+            EmojisListeningThreadTimer.Interval = 10000;
             EmojisListeningThreadTimer.Start();
         }
 
@@ -1052,14 +1091,7 @@ namespace ChatController
         // Wird im BeWoPlaner benutzt
         public Contact GetCurrentContact()
         {
-            if(AktChatUserList != null && AktChatUserList.Items.Count > 0)
-            {
-                var contact = (Contact) AktChatUserList.Items[0];
-
-                return contact.UserIdManage == null ? null : contact;
-            }
-
-            return null;
+            return CurrentContact?.UserIdManage != null ? CurrentContact : null;
         }
 
         // Wird im BeWoPlaner benutzt
@@ -1107,5 +1139,13 @@ namespace ChatController
             var view = (CollectionView)CollectionViewSource.GetDefaultView(Clientlist.ItemsSource);
             view.Filter = UserFilter;
         }
+
+        private void Chatbox_OnTextChanged(object sender, TextChangedEventArgs e)
+        {
+            if(string.IsNullOrWhiteSpace(Chatbox.Text))
+            {
+                Chatbox.Height = 25;
+            }
+        }
     }
 }
diff --git a/ChatController/HauptKlassen/Chat.cs b/ChatController/HauptKlassen/Chat.cs
index e990fe7..952bbb4 100644
--- a/ChatController/HauptKlassen/Chat.cs
+++ b/ChatController/HauptKlassen/Chat.cs
@@ -34,6 +34,7 @@ namespace ChatController.HauptKlassen
     public class Chat
     {
         public Action<Exception> ExceptionCallback { get; set; }
+        public Action<Exception> ThreadExceptionCallback { get; set; }
 
         private readonly List<Contact> _Contacts = new List<Contact>();
 
@@ -49,10 +50,11 @@ namespace ChatController.HauptKlassen
 
         public long LastTimeStamp { get; set; }
 
-        public Chat(ChatDatenUebergabe chatDaten, Action<Exception> exceptionCallback)
+        public Chat(ChatDatenUebergabe chatDaten, Action<Exception> exceptionCallback, Action<Exception> threadExceptionCallback)
         {
             ChatDaten = chatDaten;
             ExceptionCallback = exceptionCallback;
+            ThreadExceptionCallback = threadExceptionCallback;
         }
 
         // WebRequest
@@ -82,14 +84,7 @@ namespace ChatController.HauptKlassen
         {
             try
             {
-                var bitmapImage = new BitmapImage();
-                
-                bitmapImage.BeginInit();
-                bitmapImage.UriSource = new Uri(pUri);
-                bitmapImage.CacheOption = BitmapCacheOption.OnDemand;
-                bitmapImage.EndInit();
-                
-                return bitmapImage;
+                return DownloadImageWithRestRequest(pUri);
             }
             catch (Exception exception)
             {
@@ -98,6 +93,38 @@ namespace ChatController.HauptKlassen
             }
         }
 
+        private ImageSource DownloadImageWithRestRequest(string uri)
+        {
+            Bitmap bitmap = null;
+
+            if(!string.IsNullOrWhiteSpace(uri))
+            {
+                var client = new RestClient(uri);
+
+                var request = new RestRequest(Method.GET)
+                {
+                    ResponseWriter = responseStream =>
+                    {
+                        try
+                        {
+                            bitmap = new Bitmap(responseStream);
+                        }
+                        catch(Exception exception)
+                        {
+
+                        }
+                    }
+                };
+
+                request.AddHeader(Constants.Token, ChatDaten.AuthToken);
+                request.AddHeader(Constants.CustomerId, ChatDaten.Kundennummer);
+
+                client.DownloadData(request);
+            }
+
+            return bitmap != null ? Utils.ImageSourceForBitmap(bitmap) : null;
+        }
+
         // WebRequest
         private void LoadMessagesFromServer(long pGroupId)
         {
@@ -131,10 +158,12 @@ namespace ChatController.HauptKlassen
                         }
                     }
                 }
+
+                ThreadExceptionCallback?.Invoke(null);
             }
             catch (Exception exception)
             {
-                ExceptionCallback?.Invoke(exception);
+                ThreadExceptionCallback?.Invoke(exception);
             }
         }
 
@@ -321,11 +350,12 @@ namespace ChatController.HauptKlassen
 
                 var messageCounter = JsonConvert.DeserializeObject<MessageCounter>(responseFromServer);
 
+                ThreadExceptionCallback?.Invoke(null);
                 return messageCounter.MessageCount;
             }
             catch(Exception exception)
             {
-                ExceptionCallback?.Invoke(exception);
+                ThreadExceptionCallback?.Invoke(exception);
                 return 0;
             }
         }
@@ -521,7 +551,7 @@ namespace ChatController.HauptKlassen
             {
                 var openFileDialog = new OpenFileDialog
                 {
-                    Filter = Resource.OpenFileDialogFilter_Test //Resource.OpenFileDialogFilter_DocumentsAndImages
+                    Filter = Resource.OpenFileDialogFilter_Test
                 };
 
                 var result = openFileDialog.ShowDialog();
diff --git a/ChatController/LoginControl.xaml.cs b/ChatController/LoginControl.xaml.cs
index 18e5b72..15b97af 100644
--- a/ChatController/LoginControl.xaml.cs
+++ b/ChatController/LoginControl.xaml.cs
@@ -90,6 +90,13 @@ namespace ChatController
             DataContext = this;
 
             LeseDateiFallsVorhanden();
+
+#if DEBUG
+            _Kundennummer = "4368658436";
+            _ChatCode = "ZMCKb-BckTt";
+            _Benutzername = "muellerp";
+            Password = "F5aTk9Co47JFJCWB2Z7Y";
+#endif
         }
 
         private void AnmeldenButton_OnClick(object sender, RoutedEventArgs e)
diff --git a/ChatController/Ressourcen/warning-exclamation-mark.png b/ChatController/Ressourcen/warning-exclamation-mark.png
new file mode 100644
index 0000000..acc0847
Binary files /dev/null and b/ChatController/Ressourcen/warning-exclamation-mark.png differ