Could you explain your problem in mode detail:
- does the mouse cursor change or does the loading sign of the RadWindow appear?
- can you still click on the page and interact with it when this happens or does the browser actually freeze?
I am not aware of such a problem in the control which is why I would advise that you post the full code we can use to reproduce the problem in order for us to inspect it.
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