UPDATE: Nintendo have released a patch for this now, which can be downloaded from the eShop. If your game glitched, downloading the patch will allow you to continue without resetting.
A major bug has been found in Pokemon X&Y. If you save your game at certain places in Lumiose City and reload the game (i.e. turn your 3DS off and come back to the game later) then you will be stuck! This only happens in the outside areas, on the circular boulevards surrounding the city. Saving the game inside buildings such as Pokemon Centers works fine.
Nintendo have acknowledged the issue and are working on a fix, which will be made available via the eShop as soon as possible. If you have already experienced the issue you can wait for the update, otherwise you will need to restart your game. Nintendo have released this map showing you where NOT to save:
