It is possible to insert only RadDocks in a RadDockZone control. The dock zone expects controls of type RadDock
in its content because its purpose is to enable areas of the page in which docks can be placed.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed