Once a Pokémon is forcefully retrieved from the system, the Pokéwalker which holds the Pokémon's details is unusable. A Pokéwalker's settings must be deleted and reset before making it usable again. Delete and reset the settings on the game by pressing and holding Down, X, and L at the Pokéwalker connection screen. This must be done to avoid cloning and glitches to occur in the game. After resetting a Pokéwalker, it may be synced with another game, or a new file.
It should also be noted that when synced with a new game, the Pokéwalker will become the language the game is. For example, if one synced a Pokéwalker that came with a Japanese game with an English game, after syncing, the Pokéwalker would be in English. This proves that very little data is stored on the Pokéwalker itself, most likely that only the Pokémon on it and the trainer's party is stored on it. The latter could be because players can fight up to 10 trainers they have gifted with at the Trainer House in Viridian City.