When you are sending sample projects please open support tickets instead of forum threads.
As the property is called this is the margin of the restricted area. That means that the restricted area 10, 10, 800, 800 is smaller than the restricted area 10, 10, 600, 600, as these are the distances from the end of the Silverlight plugin to the end of the restricted area. Please, find the attached image that explains the RestrictedAreaMarign property.
The exception is thrown, because the restricted area itself has negative width or height.
the Telerik team