Halo 3 Marathon Man Achievement?

[Noah]

I have done it atleast 5 times but i don't get achievement. I watched it till the end (past red screen) (on the fourth terminal it doesnt give you the red screen). I did it on Normal and with a friend(do we have to do it single player?).

 

[brett c]

ya you have to do it in single player its kinda gay how they made that