Cant Log-IN 2 Users at the same time

I was wondering if anyone could possibly help me with this strange problem.

As of recently, I cant have more then 1 person logged in at a time. I can switch users and pick the second user, but the screen just quickly flashs the first logged in person's desktop, then back to the login screen.

If I log off the first user, I can log into the second no problems.

I am using Windows XP Pro with Sp2. All up to date. Also running Norton Internet Security 2005.

 

Well I seem to have fixed it. I did a system restore back a few days...I think I know what it was, but not sure why it happened. I recently downloaded a windows update for my video drivers. That must have been the problem.

 

Ensure fast user switching is enabled.