Eh bro i got the same prob. U KNOW WHY OR NOT. kkk. i took 40-50 times to figure this shit out. Basically when u use the rapid fire hack, up to 3 guns will be activated under the rifles column.
So to solve this problem,
1) log in to ur account
2) GO to storage
3) Activate only 1 gun (e.g mp5) and this automatically deactivates ur AK-47 + 2 other guns that have a *Use* sign on it
4) Enter the game and enjoy.