Nintendo is working on a fix for a bug in Pokémon X & Y that renders saved files unusable when a player saves in certain areas of Luminose City.
The update on their Japanese website says they are hoping to address the issue with a fix in the next few days.
They advise you to save in buildings such as the Pokémon Centre, and to avoid saving in the blue areas highlighted on the map below.
The fix will apparently deal with the corrupted files as well, so if you are happy to wait the few days, you may not have to restart the game.
Have you encountered any problems? Let us know in the comments.