1- Move your gamer profile to a memory card or USB storage device.
2- Start the game and at the Paradox interactive screen pull the USB device from your console.
3- Ignore the prompt to put it back in and start the game.
4- If done correctly all your campaign progress should be gone and it will show that you have 0 achievements.
5- Put the USB device back into your console and let it sync up. It should now show whatever ach's you had before.
6- Repeat the requirements for the glitched achievements and they should all pop.