The RadWindow's content is moved in the DOM and the update panels use the innerHTML property to work, thus they often cannot find the content they need to update if the entire RadWindow is placed in an update panel. If you are loading an entire page in the RadWindow you can use AJAX in ti separately from the main page and you would not need the ajax panel in the first place. If you need to modify some settings of the RadWIndow you can do so via its client-side API
. If you are using the ContentTemplate I would advise that you place the ajax panel directly inside it, so that it wraps only the contents of the RadWindow, not the entire RadWindow. Also, please make sure that the controls you change in the code-behind are actually updated on the client, as if they are outside of the RadAjaxPanel the change would not be reflected on the client, and this is a probable cause why it would seem that the event is not fired.
If you are still experiancing difficulties please open a support ticket and send us a runnable project that isolates this behavior so we can investigate it.
the Telerik team