Have you edited any ULX code?
Do you have any lua files in non-addon format in gmod/lua/autorun or autorun/server?
I'm really at a loss.
If there were really an issue with ULX, there should be an error in console on server load, or at the least when you attempt to run the chat command.
I've tested latest SVN and have no issues with it in single player (other than my server.ini commands not running; mentioned in another thread.)