Switching Users

[Nick]

I have a problem when I try to switch users. If i hit
switch users, then select the new user, the screen
flickers, showing the wallpaper of the old user, then goes
back to the logon screen. I have to logoff completely in
order to get to the other users. Can someone please help
me? Why is it doing this. I had to reinstall the OS. It
never did this before.

Thanks,
Nick