Play the mission "Moral Fiber" normally
Upon reaching the warehouse (after the convoy is ambushed) fight along with your squad to secure the area
Once the area is secured you should receive a radio transmission from Nikos (Sorry, I probably spelled his name wrong) regarding you needing to call off the artillery strikes.
Once reinforcements arrive you are directed to board the vehicle you were in earlier (marked by a waypoint)
Once you enter the vehicle it will begin to make its way to the squad that is under attack
You will receive another transmission from "Crossroads" along the way
Once the vehicle arrives at the squad that is under attack, you will be disembarked from the vehicle
It is at this point the issue triggers. Your team leader (sometimes) will issue a regroup command (he will be in a vehicle ~700m behind your position), and the mission will fail for "Not following orders"