sv_cheats? offline zombies solo?

hi guys found the code for sv_cheats which is 297A658 in CE and everytime i activate it it gives an error of invalid IWD. two things... how can i do sv_cheats 1 without getting an error or is there a way yet to play zombies solo offline (no internet connection).

Edit: also certain things like fullbright and noclip wont work unless sv_cheats is enabled

So how does this work?
Can we get offline zombies to work this way.

^ Thats what i've been trying to do.