Ran into an issue on a website where the Session was timing out yet the forms auth ticket was still valid which was causing errors. Here is one solution:
http://dotnethitman.spaces.live.com/blog/cns!E149A8B1E1C25B14!210.entry
The GU also mentions some of this in the post and in digging through all the comments.
http://weblogs.asp.net/scottgu/archive/2005/11/08/430011.aspx
About the Author