If you are using .Net 2.0 it is likely you've hit this bug
. If this is the case you can check the following article for a workaround:
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?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.