I am not sure what might be causing the problem with populating the specified DropDownList on your side. There is a sample project (a modification of the MyPortal demo) attached to the thread, that I think will help you resolve this issue. If you are still experiencing difficulties finding a solution, can you please open a new support ticket and send the full source code of your project? We will be glad to help you.
All the best,
the Telerik team