A maintenance period for the Pokémon Global Link will take place at the beginning of November which will affect Code Redemption. During the maintenance, players that have received codes via promotions will not be able to redeemable them in Pokémon X or Pokémon Y. This maintenance period will start on the following days:

US: Monday, November 3rd, 2014 until Wednesday, November 5th, 2014
UK: Tuesday, November 4th, 2014 until Thursday, November 6th, 2014

Source: http://3ds.pokemon-gl.com/information/3b37138b-6993-4bd0-858e-900efa72fdc7