Hello Sodi We,
This is strange. Please see a short video I have just made with VS 2010 here
Please check whether the version of the Telerik assemblies ends with .1040 which means it is built against Silverlight 4.
the Telerik team
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items