Hey folks, I get what i'm supposed to do in the start of the fourth mission, but everytime I choose a target for my Whirlwinds they fire once then try to move and they never re-load.

What am I doing wrong?

LOL, at the beginning of the 4th mission you just need to tell them to attack the ground! Once you kill off all the guys who are in range of your whirlwinds, send your Aerial Marines (Can't remember what they are called) in to finish them off, then your real mission can begin.
If you can't seem to get past that part, then I guess you need to update, although that might reset your saves.