If it is just you having the issues and no one else, make sure you don't have a local copy of ULX or ULib installed in your addons folder. I don't know if they would interact and cause problems, but it might. Also, make sure you have cl_allowdownload set to 1 so that you can download the client files from the server.
If All of that failes, on YOUR client (assuming its just you having issues) remove your:
garrysmod\cache
garrysmod\download
garrysmod\downloads
folders. Restart GMod and rejoin the server to get fresh copies of all the client lua files.