1) What was seen in the console? What were the last few messages?
If you have dedicated server, run it with condebug and see what the last few lines in the console.log say.
2) Do a search on your hard drive for ulx (folder). I've seen steam squirrel away copies of things in odd places (like under Valve). Maybe the copy of ulx or ulib you're deleting isn't the only one or isn't the one that it is using?