have you downgraded or upgraded since you started playing?

 

i did nothing i was playing yesterday i saved the game i shut down my 3ds i slept then today i started the game and got the message

 

yes i did

here is the save file

 

eur

 

as far as I know there's not a way to fix this. I would just wait a few days and play again, I know the frustration of losing a game save, I would suggest making backups every once in awhile. and whenever you are done with a game, press home and close the game before powering off.