Last week Microsoft started rolling out the ability to enable two-factor authentication on your Microsoft Account (read more here if you don’t know what this is). This adds another layer of security to your account prompting you for two forms of authentication before you can log in to your account. Of course not all applications/sites currently support this so there are ways to get your old stuff working.
One of these is Xbox LIVE and the nice folks over at playXBLA have posted a handy guide on how to get your account logging back in if you have enabled this option.
Read it here.