thank you for your reply.
you can reproduce the error with the code below.
Telerik.Windows.Controls.RadWindow f = new Telerik.Windows.Controls.RadWindow();
f.Content = new C1.Silverlight.Maps.C1Maps();
C1.Silverlight.Maps.C1Maps is ComponentOne's silverlight map. you can get it from link below.
try to zoom in and move the map in RadWindow. you should get the error and I.E. crashes.
as i said, it worked before upgrade. so currently, i have to downgrade to the previouse RC.