IVe got the exact same problem and am missing a couple of tabs in my XGUI, How did you guys resolve it?
Just so everyone else knows, the problem was being caused by an older version of ULX being installed in a different location on the server (in his case, directly inside the garrysmod folder)
Basically, make sure you have latest SVN version, installed properly on the server, of both ULX and ULib.
Make sure you don't have old copies installed elsewhere on your server.
Make sure your server is sending files to the client.
Make sure your client is downloading, and running the proper files.