Could you please elaborate more about the issue with the window opening? What is the actual and the expected behavior of the control?
For the time being I can suggest that you examine the following resources that may be helpful:
- Open RadWindow from the server - http://docs.telerik.com/devtools/aspnet-ajax/controls/window/troubleshooting/opening-from-the-server
- Load UserControls via AJAX - http://docs.telerik.com/devtools/aspnet-ajax/controls/ajax/how-to/load-user-controls
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