idk i think you need HL2 EP2 content :/

вашу мать я ♥♥♥♥

i have the same problem.

When in Garry's mod main menu look to the lower right when you see a tab that says games click on it make sure you have your Half Life 2 Ep. 2 enable cause if it's not it will cause these error's so if you then restart Garry's mod and rerun the map.