Ok, totally stepping out on a limb here.
Did you try manually editing any user files? (Don't, if you did. Delete them - if you edited any of our txt files in /addons/<?>/data/, you didn't read the top instructions of them)
Does the user Gmod is running under have write/read access to your <server gmod>/data/ folder.
Can it read, if it existed, your <server gmod>/settings/users.txt file?
Just from a quick scan, it seems most of the commands the load of ULX is choking on are deaiing with loading of groups.txt, which, if corrupted, and for some reason, ULX can't correct or create blank (we try in a few different ways), it may be returning the errors you see.
(This is just my educated guess...Megiddo/Stick may be able to look at the errors and see more)
Also, and this is even more conjecture than educated guess... Megiddo's finding of the way
changing gamemode and map at same time breaks things may be affecting Linux even worse, including at startup.
I'd hoped someone out there may also be running linux, and could tell us if they see the same problem on a clean install of Gmod, ulx, ulib.
(or even a non-clean install, but, clean is easiest to troubleshoot up front)
