Error screen

[I beat Chairs]

Whenever I load into the server, my screen is just an error. I have CSS and CSGO downloaded and mounted, I also have the whole collection downloaded. I've tried restarting my GMOD and PC multiple times, Ive tried deleting GMOD and reinstalling but nothing is working, If you had this problem before please help me out

 

[Dibbly Dipperson]

I might be wrong, but I think you need half life 2 downloaded, maybe. If not then there could be out-of-date drivers causing the error. Hope you fix it.

 

[A Sack O' Salt]

Although I agree with @Dibbly Dipperson , it may be because of an addon file is corrupted.
Unsubscribe from all workshop addons, delete all currently installed workshop addons from steam apps->Garry’s Mod-> Garry’s Mod->addons, then open the game again, make sure you’re installing all custom files from server in Options->Multiplayer, hit apply, rejoin again.