When you change profiles in outlook youyr activesync application will barf when next trying to sync because its a different outlook profile.

The following link shows how to reset the activesync profile to use the new outlok profile. If you dont follow these instructions nothing short of an uninstall/reinstall is required for the activesync, which is painful to say the least!

http://www.pocketpcfaq.com/raj/WM5Profile.html