For some reason, about every 3rd or 4th Iron Banner match I play, halfway through the match, all of a sudden I'm playing a secret zombie level. They're walking around aimlessly, into walls, and off of ledges. I shoot at them and they pay no mind. It doesn't even damage them. Then all of a sudden, my screen goes black. Then I'm sent either back to orbit, or sometimes the main title screen. How do I beat this mission? Am I not using the right weapons or what? How do I damage the zombies? And how do I keep from getting kicked out of the mission, do I have to kill a certain amount of zombies in a certain time frame or what? I'm totally lost! Can someone please help?