Fribble, this was recently found on a server due to an SVN update where Megiddo failed to unlink a file that had been removed..
Recent SVN versions should have fixed this.
Are you running SVN? Is it the latest?
Are you running dedicated server?
Or listen server?
Also, if you are running latest SVN and are connected to your dedicated server, it is possible and likely that a mod you have installed (but your admins may not) is out of date (or just plain written badly) and causing issues with ULX.