in ASP.NET 1.1, I want to keep my session alive for a while.

I add an object to session (Session.Add()) and set the session timeout in the web.config for 20 minutes however it seems to lose the session after 5 minutes (well before 20 minutes) or after a few refreshes of the page.

any ideas how I can keep the session alive for longer fully until the time specified in the web.config?