"Server is using different class tables"

That message pops up every time i try to join any server.
Any tips?
Things i have done

§Rebooted computer
§Verified integrity of game cache
§defragment cache files

“Server is using different class tables” means the server is using a different version of Garry’s Mod than you do.

Usually when there’s a new update to Garry’s Mod, many servers have this problem because they don’t update automatically (I think?).

If you are using the real, proper Steam version, it will update automatically - it’s not your fault, it’s the server’s fault.

Are you sure that this message pops up when you join ANY server? I highly doubt that.

Im using the version i bought of steam, and any server im trying to connect to says that, and my GMOD was lastly updated 10th September

That’s weird.

Are you only trying to join empty servers, maybe?

Servers that are outdated will (almost?) always be empty, since no one will be able to join them - try joining a server that has 10+ people playing on them and tell me if you still have that problem.