It is important to note that there is a bad save bug on the Xbox One that has affected some users.  On CD Projekt RED’s forums people have reported this issue.

The main cause seems to be the Xbox One’s Instant On feature and the bug mainly occurs when a game is resumed from this state.

CD Projekt RED has recommended you manually close the game once you’ve finished playing by going back to the dash and then using the option menu to end the application.

More info on the bug can be found here – http://forums.cdprojektred.com/threads/38160-Xbox-One-quot-You-cannot-save-your-game-right-now-quot-Any-word?p=1684991#post1684991

Apart from this it is a brilliant RPG and a must play.