While visiting Asp.net forum I found a lot of request on how to show a different page when the asp.net session expires. The following line will exactly do the same:
HttpContext.Current.Response.AppendHeader("Refresh", Convert.ToString(((HttpContext.Current.Session.Timeout * 60) - 5)) + "; Url=YOUR PAGE WHICH YOU WANT TO SHOW");
It simply injects a meta data which refresh the pages in the client side. If you are using any master page you can add this line in the PreRender event
