Do Escort Duty on SOLO. the same applies for all other rewards - solo only!!!!!! I had the same problem and finally tried solo and it worked!!!
The trick to completing Escort Duty is to have the engineer class, obviously, but I had the turret that I could deploy (by going under abilities @ main menu, and then under the engineer section). As well as turrets, I'd place mines infront of doors before enemies came out. DO ALL OF THIS B4 U REPAIR TRUCK TO GET IT MOVING @ BEGINNING. Once the enemies come, it becomes harder, although possible, to deploy these things.
Good Luck
