Thanks I'll try it again. I watched a you tube walkthrough for this and the player completes it in one try. He selects the same enemies I do and locks on them. He only shoots the enemy in front of him and completes it ok. I presume his team kills the others, why mine don't do this has got me stumped.
I did the same and did it in first try also, But I marked the enemies in the same sequence as the you tube walkthrough.1.Mark bottom right man,2.mark top right man man,3.mark bottom left man,4.mark top left center man. then hit f to lock targets and shoot the bottom left man.