The ASP.NET AJAX UpdatePanel gets updated in one of 3 ways.
1.) An implicit control event triggers an update (that is a control inside the UpdatePanel is getting updated, etc.)
2.) The UpdatePanel has a <Triggers> Collection, and one of the defined triggers gets fired.
3.) The UpdatePanel’s Update metod is explicitly called in the course of some server side logic.
Ceck out his link on CodeProject for a solution.