I just got Halo 3 and starting campaign, I finished missions 2 and 6 but didn't...

[kimmelj17]

...get the medal. Any ideas? I went into 3 and got the medal and achievement points and same as 6 into 7. It's been on the same level, could I have done something different to move on, but not the correct thing?
I have kept in on normal

 

[Trevor D]

you have to do it perfectly it was unbelievably hard for me when i did it the first time

 

[ScareBear]

change the difficulty level for those missions, you need to be on normal, heroic, or legendary to get the achievement points