On opening the popup from the server I advise you examine the following sticky thread: http://www.telerik.com/community/forums/aspnet-ajax/window/opening-radwindow-from-the-server.aspx
. The script registration or disabling the ViewState should work for your case.
can also be useful on hooking the OnClientClose handler individually for each user control instance to prevent functions with the same name from overriding each other. There are many other ways to initiate a request to the server that depend on the current case. This blog post
can be interesting in this regard.
the Telerik team
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