Need help with a model error

I was like so pumped cause i haven’t played gmod for like 6 years. so i loaded up the game, (also team fortress, counter strike source and halflife 2 cause it said i needed to), clicked on single player then double clicked on one of the gmod maps. it went to the loading screen, then the game crashed and i got an error message: model Models/props_buildings/buildingskybox_002a.mdl not found and models/error.mdl couldn’t be loaded. It is titled engine error. help. please.

You don’t need to have TF2, CS:S, and HL2 open at the same time that Garry’s Mod is. I suggest going to the “GMod Settings” button on the main menu. Check all the games that you want to add things from, and restart Garry’s Mod.