Since the RadAjaxPanel extends the standard MS UpdatePanel, have you considered setting the AsyncPostBackTimeout
property of the asp ScriptManager instance to define the timeout period or the ScriptTimeout
property of the HttpServerUtility object? Reviwe the following ASP.NET forum threads which elaborate on this subject:
This should be sufficient for RadAjaxManager as well since it dynamically injects MS UpdatePanels around the updated controls "behind the scenes".
the Telerik team