Why can't i play First Strike Offline?

I have tried everything....

Redownloading the map pack, playing in split screen and solo whilst connected to XBL, When i unplug my cable and turn of my wireless, it doesn't boot me out of the game, it still let's me, but when I am not connected to XBL, I don't get the Zombies Map and the Multiplayer maps (First Strike ones) and i can't play them??

Any help please?