On The Halo 3 campaign help?

[mike k]

I saved and quit on the campiagn mission "the ark" i went back to it and went to a check point and i finished to mission but i didn't get the achievment
i also tried doing it from that checkpoint 2 other times which altogether equaled like 3 times but it didn't work

 

[ad_am_sy_ed_xd]

dont know did you try to do it again?