We do not have such a sample ready and RadControls for ASP.NET AJAX are not tested under MVC and we do not support it, I am afraid. They are built on top of the webforms paradigm and heavily rely on its lifecycle, which is not available elsewhere.
Nevertheless, you can consider a WebUserControl that has this RadWindow. In the code-behind of the user control you can check if the user is logged in and if not - do show the RadWindow: http://www.telerik.com/community/forums/aspnet-ajax/window/opening-radwindow-from-the-server.aspx
. I cannot guarantee it is possible and that it will work as desired, but I hope it will.
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