Still no answer halo 3 achievement!?

[Anna C]

OK so I get 50000 pionts at the end of the level and i am useing gold and white skulls and team scoreing is on because i am playing with my friends and at the end of the level none of us get the achievement! (we are playing on legandry)

 

[godackz]

what lvl is it?

 

[Ryan O]

Mabey You cant achieve it on Co-Op , i got that achievment when i was playing by myself.