Added check if parent view is ContentControl to avoid exception when pasting on for example a Border, that have a content property but is not a ContentControl.

src/AddIns/DisplayBindings/WpfDesign/WpfDesign.Designer/Project/Xaml/XamlEditOperations.cs

@@ -131,7 +131,7 @@ namespace ICSharpCode.WpfDesign.Designer.Xaml
 								AddInParent(parent, pastedItems);
 								pasted = true;
 							}
-						} else if (pastedItems.Count == 1 && parent.ContentProperty.Value == null && parent.ContentProperty.ValueOnInstance == null && DefaultPlacementBehavior.CanContentControlAdd((ContentControl)parent.View)) {
+						} else if (pastedItems.Count == 1 && parent.ContentProperty.Value == null && parent.ContentProperty.ValueOnInstance == null && parent.View is ContentControl && DefaultPlacementBehavior.CanContentControlAdd((ContentControl)parent.View)) {
 							AddInParent(parent, pastedItems);
 							pasted = true;
 						}