* The Pokéwalker has already been registered to another game. Each Pokéwalker can only be registered to one game at a time. If you have previously registered your Pokéwalker to another game, you will need to unregister it before you can register it to your current game.
* The Pokéwalker is not compatible with your game. The Pokéwalker is only compatible with Pokémon HeartGold and SoulSilver. If you are trying to connect the Pokéwalker to a different game, it will not work.
* The Pokéwalker is not turned on. Make sure that the Pokéwalker is turned on before you try to connect it to your game.
* The Pokéwalker is not in range of your game. The Pokéwalker must be within 3 feet of your game in order to connect.
If you have checked all of these things and you are still getting the message that the Pokéwalker has already been registered, you may need to contact Nintendo Customer Service for assistance.