I am not aware of your specific scenario, but I reproduced the behavior by dynamically creating RadDock and RadDockZone controls and adding them to a WebUserControl. The UserControl itself is added dynamically on a Button Click. At first, the client-code was placed in the markup of the UserControl and I was getting the same error - the handler method is not defined. To overcome the problem I registered the script dynamically from the server using the ScriptManager.RegisterStartupScript
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