What aspects of the UpdatePanel are sensitive to time?
I have an UpdatePanel that works fine. If I leave the page for a few minutes and come back, the UpdatePanel doesn't work. Looking at firebug, I see that it sends the Request and gets a Response back. However, the page itself doesn't update. I'm not seeing any script errors either. So far I haven't been able to identify any other factor than the passage of time.
Maybe your application domain recycled or your Session was lost. Have you tried seeing what is being called on the server? That'd be my suggestion on where to look next.
Most likely the session expired, causing it to send back data that no longer matches the page.
If it's a session expiring, it should be reproducible without the UpdatePanel -- go back to postback and see if it also happens that way. You might even get a better idea of the error since it isn't potentially eaten by the JavaScript that the UpdatePanel runs underneath the hood.
I've noticed that if you have a TON of controls in your update panel, it can either timeout or refuse to work. One time I had a gridview in an update panel with three ajax calendar controls in each row.. total of 2,000 records in the gridview.. updatepanel was none too happy
i have the same problem too. the weird part of this, time doesn't always same. sometime it takes 20 minutes sometimes 5 minutes..