<views:MainView/>
<Window/>,
а когда я добавлял Grid, то у Window было 2 дочерних элемента, а так нельзя, поэтому и лезла ошибка. чтобы это решить я закинул <views:MainView/>
в Grid и о чудо все заработало! всем спасибо! An error occurred while initializing the frame's content
System.ArgumentException: Failed to get the editor factory manager for 6d5344a2-2fcd-49de-a09d-6a14fd1b1224.
at Microsoft.VisualStudio.PlatformUI.Packages.ShellService.EditorFactories.EditorFactoryRegistrar.d__16.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.VisualStudio.Platform.WindowManagement.WindowFrame.<>c__DisplayClass75_0.<g__GetEditorFactory|0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()