Hossa, we've seen this question several times on the forum. All but once, it was a conflicting mod.
Unfortunately, as many times as I've seen this problem, only ONE person was kind enough to let us know/take the time to find out and report back.
http://forums.ulyssesmod.net/index.php/topic,1169.0.html <-- GCombat broke ULX feature.
If you temporarily remove Gcombat, restart your server, and that doesn't fix it, you may with to 'clean' your groups.txt file...I'd start with removing the 'deny' ulx physgunplayer from all groups.
User gets inherited by ALL other groups, and even if it doesn't fix the main issue, it could cause problems for the superadmin group having physgunplayer access.