Yes - I am testing with the sample portal that ships with 5.0. After adjusting the slidingexpiration, still had the issue. Bumped up the apppool recycle time to 360 - currently, no more issue. I have read that there is an issue with using a dynamic machine key and form authentication in Windows 2008 that I will be investigating today/tomorrow. Current environment is Windows Server Standard X64, IIS 7 running chat in DefaultAppPool. Dual Core 2.6G w/ 8 GB RAM connected to clean install of SQL 2008 Standard. Resources are not an issue, so checking all other avenues.