Object reference not set to an instance of an object

Dear Tanya,

 i have created a little demo project to reproduce this behavior because i m getting the same exeption. I´m using the Version 2014.1.224.45 of your Controls.

you can download the Demo Project here:

*Edited by administrator*

the Exception is only thrown if i open the control in a dialog like in the demo project and if the pdf Viewer control is on a hidden tab when i close the dialog.

1. Start the demo Project

2. Click the start Button

3. After Dialog opened select on the first tab a file from the grid

4. switch to the third "file preview" tab -> preview is shown in the pdfViewer control

5. switch back to the secound "some setting" tab and close the dialog

6. and there you go ... here is the Exception ;)

here is the StackTrace:
   bei Telerik.Windows.Controls.Input.FocusScope.FocusInternal()
   bei Telerik.Windows.Controls.Input.FocusScope.FocusNextElement()
   bei Telerik.Windows.Controls.Input.FocusScope.RemoveFocusableElement(Control element)
   bei Telerik.Windows.Controls.Input.FocusScope.FocusableElement_Unloaded(Object sender, RoutedEventArgs e)
   bei System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
   bei System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
   bei System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
   bei System.Windows.UIElement.RaiseEvent(RoutedEventArgs e)
   bei System.Windows.BroadcastEventHelper.BroadcastEvent(DependencyObject root, RoutedEvent routedEvent)
   bei System.Windows.BroadcastEventHelper.BroadcastUnloadedEvent(Object root)
   bei MS.Internal.LoadedOrUnloadedOperation.DoWork()
   bei System.Windows.Media.MediaContext.FireLoadedPendingCallbacks()
   bei System.Windows.Media.MediaContext.FireInvokeOnRenderCallbacks()
   bei System.Windows.Media.MediaContext.RenderMessageHandlerCore(Object resizedCompositionTarget)
   bei System.Windows.Media.MediaContext.RenderMessageHandler(Object resizedCompositionTarget)
   bei System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   bei System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   bei System.Windows.Threading.DispatcherOperation.InvokeImpl()
   bei System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state)
   bei System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   bei System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   bei System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   bei System.Windows.Threading.DispatcherOperation.Invoke()
   bei System.Windows.Threading.Dispatcher.ProcessQueue()
   bei System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   bei MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   bei MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
   bei System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   bei System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   bei System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
   bei MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
   bei MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
   bei System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
   bei System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
   bei System.Windows.Application.RunDispatcher(Object ignore)
   bei System.Windows.Application.RunInternal(Window window)
   bei System.Windows.Application.Run(Window window)
   bei System.Windows.Application.Run()
   bei TelerikPdfViewerExceptionDemo.App.Main() in c:\Users\anoga\Documents\Visual Studio 2013\Projects\TelerikPdfViewerExceptionDemo\TelerikPdfViewerExceptionDemo\obj\Debug\App.g.cs:Zeile 0.
   bei System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
   bei System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
   bei Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
   bei System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   bei System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   bei System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   bei System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   bei System.Threading.ThreadHelper.ThreadStart()