User locks PC, after 30 min it says administrator is logged in.

Hi all!

Hope you can help me with this issue…
I’ve got a XP machine in the AD that several users use daily, the problem is just that if a user logs in, works and the locks it when going to lunch for example, when she/he gets back it says Administrator is logged on and
that’s the only one that can logg off…
The solution has been power off for a while but that’s no good..
I’ve checked with several antivirus sw
Hijackthis
Gmer
Malwarebytes Anti-Malware
Nothing about a virus…

I’ve removed everything that has to do with autolocking screensavers and stuff like that..
Still happens…

Any idea?? I’m fresh out of them… 😀

TIA!