problem of UpdatePanel with legacy code

The page has UpdatePanel control also has many custom controls written under aps.net 1.1. After use command 'iisrestart', the respones of the first time access is correct. UpdatePanel works very well. But when we access the site again, there will be some 'access denied' exceptions. and UpdatePanel cann't work correctly. The page still refreshs when submit something in UpdatePanel.

Thanks

Update Panel only work with the xhtml transitional code. Configure your web config file from legacy to transitional
but the first access is currect after restart IIS server. how to explain it with you theory? in my opinion, it may because of cache or some related things, doesn't it?

thanks, i'v solved it. change <xhtmlConformance mode="Legacy"/> to <xhtmlConformance mode="Transitional"/> .

this article makes it clearhttp://weblogs.asp.net/scottgu/archive/2006/12/10/gotcha-don-t-use-xhtmlconformance-mode-legacy-with-asp-net-ajax.aspx