SBS 2008 in operation for nearly 2 years. Was using Outlook 2007 on several older XP machines without problem. Recently replaced XP machines with new systems running Window 7 Professional. Periodically Outlook requests authentication credentials or notes "password required" in the lower right corner. Happens on all systems with no pattern. IPv6 has been removed from windows 7 machines, but problem occurred prior to removing IPv6.
Possibly related: IPv6 was removed to troubleshoot slow response times loading Peachtree accounting software (which doesn't like IPv6 for some reason). Performance is not significantly improved. Also in use is a tax software package that runs the application over the network via shortcuts from the PC to reference .exe's on the server (so primitive) which is supposedly Windows 7 compatable. This software is on only one machine and not constantly in use. However, when the user connects remotely through the RDP from the SBS remote access site, launching the tax software can take 4 - 5 times longer (2.5 minutes instead of a "normal" 30 seconds) but ONLY when using RDP or even when i have tested using TeamViewer.
Switch is unmanaged 10/100 24-port Netgear switch. Continuous ping tests from client to server while Outlook connection problems are experienced or durring slow launching of tax software package do not show timeouts.
Exchange is SP1 with all roll-ups applied. SBS 2008 is also current on service packs and patches. Problem has been intermittent over past 6 months or more since migration to Windows 7 systems, but seems to be increasing in frequency.