I am not quite sure I understand the exact scenario. Could you please provide more detailed information on the subject, a sample page demonstrating the issue will be of great help solving the case.
In general, RadSlidingZone is a control that can be placed only inside RadPane, which can be placed only inside RadSplitter.
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