CO-OP Campaign Save file corrupt?

[ANJUNAluke]

Me and a friend keep attemtping to play threw co-op campaign together but when we load a saved session one of us always crashes regardless of who hosts the game.
i dont know whether its the cross platform as i run windows 7 and he uses a mac?
any ideas what i can do to fix this?

[ŊЏ | Shifu]

How old is the saved game?

[ANJUNAluke]

under 24hours,
weve even tried starting one then saving and reloading and it does the same thing.