I moved an ASP.NET site running on a server with .NET 1.1 to another server running with .NET 2.0.
In one of the pages I have the following code to detect an expired
I believe your session in the web.config is being reset (getting a new SessionID for each postback)
You could try to debug this by putting the SessionID somewhere on the page (for testing) with
HttpContext.Current.Session.SessionID
This did happen on one of my websites and all i had to do was go into IIS and resave the SessionState Panel