Efilecabinet closes on drag and drop.

Get the following error and then efilecabinet crashes when trying to drag a folder from Active to Inactive Clients.

System.NullReferenceException: Object reference not set to an instance of an object.
at efcWpfCore.GUI.Client.UserControlCabinetFolderBrowser.DoDrop(TreeViewViewBase destination, MoveType type)
at efcWpfCore.GUI.Client.UserControlCabinetFolderBrowser.PART_Header_Drop(Object sender, DragEventArgs e)
at System.Windows.DragEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.UIElement.RaiseEvent(RoutedEventArgs e)
at System.Windows.OleDropTarget.RaiseDragEvent(RoutedEvent dragEvent, Int32 dragDropKeyStates, Int32& effects, DependencyObject target, Point targetPoint)
at System.Windows.OleDropTarget.MS.Win32.UnsafeNativeMethods.IOleDropTarget.OleDrop(Object data, Int32 dragDropKeyStates, Int64 point, Int32& effects)
at MS.Win32.UnsafeNativeMethods.DoDragDrop(IDataObject dataObject, IOleDropSource dropSource, Int32 allowedEffects, Int32[] finalEffect)
at System.Windows.OleServicesContext.OleDoDragDrop(IDataObject dataObject, IOleDropSource dropSource, Int32 allowedEffects, Int32[] finalEffect)
at System.Windows.DragDrop.OleDoDragDrop(DependencyObject dragSource, DataObject dataObject, DragDropEffects allowedEffects)
at System.Windows.DragDrop.DoDragDrop(DependencyObject dragSource, Object data, DragDropEffects allowedEffects)
at efcCore.Classes.DragDropHelper.SetToDrag(DependencyObject source, List`1 items, DragDropEffects dragEffects)
at efcWpfCore.GUI.Client.UserControlFolderContentDisplay.StartDrag(MouseEventArgs e)
at efcWpfCore.GUI.Client.UserControlFolderContentDisplay.xamDataGridFolderContent_PreviewMouseMove(Object sender, MouseEventArgs e)
at System.Windows.Input.MouseEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
at System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
at System.Windows.UIElement.RaiseEvent(RoutedEventArgs args, Boolean trusted)
at System.Windows.Input.InputManager.ProcessStagingArea()
at System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
at System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
at System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel)
at System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
at System.Windows.Interop.HwndSource.InputFilterMessage(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)