If you’re not joining a server – and the errors are happening on your local machine – the best way to fix this is to clean your GMod installation. The easiest way to fix the textures is to actually buy the game. A lot of mappers use materials and props from that game. Purple textures and big red flashing errors in gmod are usually caused by you not having Counter-Strike: Source. Find one you and your friends can all join and play together. Click on “Play Multiplayer” to bring up a listing of all available “GMod” servers. Load “GMod” to access the game’s main menu. In order to play “GMod” with your friends, you will need to either create a server or join an already existing server. Then, open the “garrysmod” folder and then open the “addons” folder. This will open the location of your game. Open Steam, navigate to your library, find “Garry’s Mod” and right click and select “Properties”, Goto the “Local Files” tab, click “Browse Local Files”.
Navigate to your local Garry’s Mod addons directory.