We are not quite sure what is causing the problem in your case, but I believe that this online demo
will be of help. The implementation of the DBContentProvider (used in the demo) is placed in the INSTALL_FOLDER\Telerik\RadControls for ASPNET AJAX Q(x) 2009\Live Demos\App_Code\Editor
In case that the demo does not help, please open a new support ticket and send us a full sample project which reproduces the problem that you experience. Once we have a better view over your code, we will do our best to provide a solution.
the Telerik team