When I opened Minecraft today it had signed me out so I clicked Sign In on the main screen, it brought up the Xbox Live profile with the "Let's Play" button, after confirming my account the popup closed, the game froze for a few seconds and crashed. 

(Below the menu shows the XLive popup with the "Let's Play" button and the other image is of the app stuttering in it's final moments and then closing. That's all she wrote)