Are you looking at this
demos? If so and you still get the error, could you please give us the steps to reproduce. Also, give us some more details what exactly you want to achieve with RadCalendar control. Meanwhile, you can check our online documentation
Looking forward to your reply.
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