So i dont know if this is something you have on your Gmod but make sure you arent in Chromium or something like that, I used chromium because i would go on theater servers and after I switched it back to normal all my Errors were gone so i would try that If you dont know how to Close your game completely got to steam and right click gmod, go to properties and then to the last tab which is called betas and switch it from chromium or whatever you have it currently set to and place it to opt out or none, If this doesnt fix it or your game is already set to that then change it to the other settings until it possibly fixes. other then that I have tried almost everything and this is the only thing that has worked!