Ajax and Converted VS2003 Web Apps

We couldn't get AJAX to work on any applications converted from VS2003 to VS2008 (running .Net 3.5). All the code made post backs instead of running AJAX in update pannels. After a line by line rip apart of the web.config we tracked it down to
. Searching the net Scott Guthrie has written a post explaining this.

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