Note that by design ASP.NET AJAX Framework cancels the ongoing Ajax request if you try to initiate another one prior to receiving the response from the first one. This is the only possible way to cancel one ongoing request. I'm not completely sure if the presented error is caused by processing a new request during Ajax request. Could you please post some code from your markup and the related code behind so we could further investigate the issue?
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!