As soon as a place a light_envireonment it crashes the engine, and if I change an entity to it as soon as I hit apply the engine crashes. Any idea what went wrong?
I assume the level editor - Hammer - crashes, and not the whole engine. As for that, I’d simply advise to verify game cache files for the SDK or reinstalling it, as that should not happen.
Which Hammer are you using? I was just using Source SDK 2013 Singleplayer earlier today and the game crashed when I opened a map. IDK if it’s also acting up for you from the new Gmod update, but I can help you fix it if it is.