Error models and pink looking null squares?

I just got garrys mod, and almost every server i go in to i get error models and pink looking null squares.I tryed turning my anti-virus software off and reinstalling garrys mod, but i still get this problem. Can someone help?

Do you have Css? Also, most people use phx so try and download that

Try getting Counter Strike: Source, PHX mod, Wiremod, and (maybe) Stargate Addon Pack

Ok i’ll download the add-ons, but didn’t know i needed to have CS:S…

You don’t NEED it, but mappers and swep makes use the textures/models a lot so it is a very good addition. (I myself bought it only for the models/textures, I hate the game itself)