System.InvalidCastException
Unable to cast object of type 'Intersoft.Client.UI.Aqua.UXDesktop.UXMessageBox' to type 'System.Windows.Controls.Grid'.
   at Microsoft.Expression.Platform.Silverlight.Host.SilverlightImageHost.get_RootInstanceWrapperHolder()
   at Microsoft.Expression.Platform.Silverlight.Host.SilverlightImageHost.set_RootInstance(Object value)
 
Microsoft.Windows.Design.Platform.InvalidDesignerUpdateException
An unhandled exception was encountered while trying to render the current silverlight project on the design surface. To diagnose this failure, please try to run the project in a regular browser using the silverlight developer runtime.

 I get the above error and VS2010 crashes - any ideas, thanks.