I was having a very hard time getting any of my achievements to unlock and I tried everything. I deleted the game and reloaded, deleted the save file, deleted the achievement history (since I had non unlocked) and nothing worked.
I even tried clearing my system cache and still no luck.
I finally figured it out and got 'em to unlock. I had purchased the game on a buddy's Xbox and then downloaded it on mine so we both could have it and play together. He was able to unlock the achievements with no issue, so I went to his place to see if mine would unlock on his system. And of course, they unlock with no issues.
I really hope this is not something the developer planned for, as a way to encourage more people to purchase the game by not allowing achievements to unlock on other counsels.
We have done this many other times with many other games and never had these problems.