Sylent, we've seen this _long_ time ago. I forget what mod allowed it, but it wasn't anything to do with ULX.
Let us see your debug output, it may help pin down the problem and find out whether it's ULX (unlikely) or not.
WHILE non-admin people are connected to your server, especially if they can pick others up
FROM the server console (or rcon), type "ulx debuginfo"
The server console should then say where it output a file. I forget where exactly, it's a gmod/data/ulx/*.txt or data/ulx*.txt file.
Attach that file here in reply.