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System.Windows.Markup.XamlParseException: Durch den Aufruf des Konstruktors für Typ "Drexel.VidUp.UI.ViewModels.MainWindowViewModel", der den angegebenen Bindungseinschränkungen entspricht, wurde eine Ausnahme ausgelöst.
---> System.ArgumentNullException: Value cannot be null. (Parameter 'key')
at System.Collections.Generic.Dictionary`2.FindValue(TKey key)
at Drexel.VidUp.UI.ViewModels.ObservableTemplateViewModels..ctor(TemplateListBase templateList, Boolean createByAccount, Boolean addAll, Boolean addNone) in D:\Daten\Matthias\Dokumente\Source\VidUp\VidUp.UI\ViewModels\ObservableTemplateViewModels.cs:line 56
at Drexel.VidUp.UI.ViewModels.MainWindowViewModel.initialize(String folderSuffix, String subfolder, UploadList& uploadList, TemplateList& templateList, PlaylistList& playlistList) in D:\Daten\Matthias\Dokumente\Source\VidUp\VidUp.UI\ViewModels\MainWindowViewModel.cs:line 452
at Drexel.VidUp.UI.ViewModels.MainWindowViewModel..ctor(String user, String subFolder, UploadList& uploadList, TemplateList& templateList, PlaylistList& playlistList) in D:\Daten\Matthias\Dokumente\Source\VidUp\VidUp.UI\ViewModels\MainWindowViewModel.cs:line 420
at Drexel.VidUp.UI.ViewModels.MainWindowViewModel..ctor() in D:\Daten\Matthias\Dokumente\Source\VidUp\VidUp.UI\ViewModels\MainWindowViewModel.cs:line 413
at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean wrapExceptions)
--- End of inner exception stack trace ---
at System.Windows.Markup.XamlReader.RewrapException(Exception e, IXamlLineInfo lineInfo, Uri baseUri)
at System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, IXamlObjectWriterFactory writerFactory, Boolean skipJournaledProperties, Object rootObject, XamlObjectWriterSettings settings, Uri baseUri)
at System.Windows.Markup.WpfXamlLoader.LoadBaml(XamlReader xamlReader, Boolean skipJournaledProperties, Object rootObject, XamlAccessLevel accessLevel, Uri baseUri)
at System.Windows.Markup.XamlReader.LoadBaml(Stream stream, ParserContext parserContext, Object parent, Boolean closeStream)
at System.Windows.Application.LoadBamlStreamWithSyncInfo(Stream stream, ParserContext pc)
at System.Windows.Application.LoadComponent(Uri resourceLocator, Boolean bSkipJournaledProperties)
at System.Windows.Application.DoStartup()
at System.Windows.Application.<.ctor>b__1_0(Object unused)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
at System.Windows.Threading.DispatcherOperation.InvokeImpl()
at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state)
at MS.Internal.CulturePreservingExecutionContext.CallbackWrapper(Object obj)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location ---
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at MS.Internal.CulturePreservingExecutionContext.Run(CulturePreservingExecutionContext executionContext, ContextCallback callback, Object state)
at System.Windows.Threading.DispatcherOperation.Invoke()
at System.Windows.Threading.Dispatcher.ProcessQueue()
at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
at System.Windows.Threading.Dispatcher.Run()
at System.Windows.Application.RunDispatcher(Object ignore)
at System.Windows.Application.RunInternal(Window window)
at System.Windows.Application.Run()
at Drexel.VidUp.UI.App.Main()
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OK
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Vielen Dank!
Danke für die schnelle Rückmeldung 
hat funktionuckelt, danke!