UpdatePanel does not working in an existing asp.net website

Spent more than 3 hours trying to make UpdatePanel to work.

Everything has been done but still does not work.

At last I searched "UpdatePanel not working" in Google, got the solution from Scott Gu.

remove xhtmlConformance mode="Legacy" in web.config file.

http://weblogs.asp.net/scottgu/archive/2006/12/10/gotcha-don-t-use-xhtmlconformance-mode-legacy-with-asp-net-ajax.aspx

I hope I searched in Google at the very first moment when I met the problem.