TheZero, as I've believed, and from what I've read, Megiddo has too since some of the beginnings of this thread, your server has old version.
The error you're getting was known in old versions, which is why we've asked you to totally wipe ULib and ULX from your server addons folder and try again.
Perhaps you've installed newer, but someway, your server has mixed files that are old.
Other than makeing sure you wipe old addons/ulx and addons/ulib and then re-install newer code, I know of no other way to help you.
Wipe your local game client addons/ulx and /addons/ulib just to be sure too.