I got right near to the end of my first playthough, when I recived an odd error
"The disc is unreadable
1. Clean the disk with a soft cloth.
2. Restart the console.
For more help, visit www.xbox.com/support"
Which is a little confusing given that I downloaded the game and there is no disk.
If anybody comes across this error, it's because your gamesave is corrupt..
I suggest you try moving your save game to cloud and clearing the cache on your xbox. This didn't work for me but I've read this solves corrupt games for minecraft so worth a shot.
To play the game again, delete your old save and cry that you have lost all your progress.