Well i beat the campaign on legendary with a friend and didnt unlock master chiefs armor skin. Does it have to be done solo or what?
bump
This is a common issue and one that is being looked into. Post the problem in the issues being investigated thread located towards the top of the Halo 4 forum and give as much detail as you can.
The easiest way to screw up the unlock is to stop playing a mission and then restarting it at a rally point.