how to avoid checking session!=null in each page load

hi,

you can create base page all you web page is inherit from this base page and base page is inherit from page

Please refer

http://www.dreamincode.net/forums/topic/45300-base-page-for-detecting-session-timeout-in-aspnetc%23/
http://codebetter.com/davidhayden/2005/03/14/asp-net-page-inheritance-base-page-classes-in-your-web-applications/

hope this will help you.