I cant start the map. There a error something like "...material_flamethrower_not_found"... can someone help me please? I really want to play this map. Ty

I have a problem with the easter egg. I play solo and at the step where i need to check the dead zombies for the code, i only get 3 letters of the code. I checked evers body. I think one of the letters was invisible when i chekced. Or i cant search a body. Did someone had the same problems? Is there...