The code seems to be fine, and I can't tell you for sure what can cause this error. Could you please explain your goals in more details? Also send us the full source code of the page or a fully working project, which will help us to reproduce the problem locally. Once we receive it, we will do our best to help you.
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.