Hey mate. Don't know if you got past it or not but that other problem posted a solution to your problem with the A-10.
Okay, I found a solution....give it a try.
Switch your keypad options when you reach the point in the scenario where you need to call in the A-10. I switched to "southpaw" but feel free to experiment. I think the act of switching your keypad inputs does the trick. Anyway, after I switched the pad's defaults to southpaw, it told me to push the left trigger to lock in on the targets for the A-10. It worked like a champ! I wiped out the tanks and then reset my options to the keypad layout I had before and continued on with the game.
Hope this helps. Hope Activision fixes this bug.