>Hi
>I am facing issue of my ASP.NET web app session expired randomly. I am using custom code to control session timeout, by using Session.IsNewSession and SessionId is existed. Once expired redirect user to session expired page.
>
>However, in some customer server, user session expired randomly. We checked session timeout setting in web.config, IIS server, process recycling after X mins, shutdown process if idle for X mins, set to use cookieless but still no luck.
>
>FYI, it is single server (2 network cards), NO load balancing. Any ideas?

First thing is to determine whether domain or app pool recycling is the cause. Are you logging these events?
If recycling is the problem then you can concentrate on finding the reasons that this is happening.
Maybe something here :
http://www.c-sharpcorner.com/UploadFile/technoNet/SessionTimeout02192009052301AM/SessionTimeout.aspx

Anti-virus ?