UPDATED:
Microsoft has announced that this glitch doesn?t necessarily lose all the achievement points, but ruins all of the structuring with Xbox.com and other web-based features that most XBL lovers have grown used to. Supposedly as long you don?t delete the gamertag from you 360 (or as long as there?s a 360 with the tag on an HDD) you should be safe, but this leads me to believe that recovering your gamertag is now impossible. As I would hope, Microsoft is looking into measures to prevent this from happening in the future to those of us unaffected.
ORIGINAL STORY
An unfortunate glitch that Microsoft has discovered may result in your gamerscore being wiped, removing any and all achievements you may have received in the last 4 years. Apparently, when you set up a Windows Live ID to create a gamertag, you must put in an e-mail address. If you choose to associate to an expiring e-mail account, like Hotmail, and then never use it (thus it expires) your gamertag will be lost with it. This may be no big deal for individuals who don?t have this issue, but for others they may quickly learn that tons of hard work are gone.
If you have a silver account, you will be keeping your gamerscore, but you can never update to gold status. It was a little complicated, but I was able to get to the main page for Windows Live and confirm that my yahoo e-mail is the associated and since I use it often have no worries about this. If you are unsure, follow the above link and check it out before it?s too late. Microsoft suggests, currently, that the solution is to create a new gamertag with the correctly associated e-mail (something I doubt many of us want to do). Hopefully a solution will be found so that those of us with unexpired e-mails never have to worry again.
http://thatgamingsite.com/userfiles/...chievement.jpg