No Achievements in Campaign for Halo 3?

[kyle]

I have been playing co-op halo 3 on legendary and we end the game halfway through missions and then start again later. We pick up at the beginning of stages within missions, however when we finish the entire mission we are not getting achievement points. The shield is also not showing up under co-op even though we have fully completed the mission.

Do you have to play the missions straight through in order to get the achievements?
I am playing on Legendary as mentioned.

 

[gkhyde]

Are you playing to the Rally Point? If not, the game might not be registering that you've played a certain amount of the mission. But to be sure, just try playing a mission from start to finish and see if you get an achievement.

 

[Henry]

play on normal or anything higher
you cant play on easy ... easy = no achievemants

or

your game is messed up