Engine Error: There was an error creating the front

I have bought Garry’s mod but whenever I try to start it, it loads up to half, and then it crashes and there is an error message: Engine Error: There was an error creating the front.Garry’s mod 9 works fine. I have Portal 1+2,Half-Life 2 deathmatch/Episode 1/Lost coast/deathmatch source. I need help! I have tried many things!