Intrepid trainers beware! Reports are coming in about a game-breaking bug in the best-selling Pokemon X and Y that will prevent your save data from loading. The bug seems to occur when players attempt to load a file that is saved in Lumiose City. It doesn’t seem to be affecting all players, and no one is particularly sure why the bug occurs, but it has been spotted in European, Japanese, and American copies of the game.
The glitch causes the game to freeze as soon as the file loads. Music plays as normal, but the buttons and touch screen become totally unresponsive. Restarting the game does not fix it, though the game loads the title screen just fine. The glitch also seems to occur more often if you save near geometry like tall buildings or trees. It is recommended that you save inside a building or away from the city in order to keep your save file safe.
Currently, no workaround has been found. If you find yourself affected by this bug, the only option you have is to delete your save file and start over.
Source: GameInformer