The following help article treats using many RadWindowManagers on the same page and offers a solution - making sure you are using the correct manager instance to open you popups: http://www.telerik.com/help/aspnet-ajax/radwindow-troubleshooting-wrong-window-opened.html
. This should also apply to client-side event handlers.
You can also avoid using RadWindowManagers in your user controls, since RadWindows can be declared and used directly on the page without a manager, you would simply need to use $find().show() with them instead of radopen() or manager.open().
the Telerik team
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