Error!
Error prevention and placeholders in the Pokémon games:
?????????? | ????? | ! | Abnormal Pokémon | Bad Egg | Enigma Berry (Generation III) | Error! | Error codes (Generations I and II) | Error traps for damaged save data | Error traps to prevent impossible progress | Event data debugging messages | Instant victory effect (Generation II) | Mystery Zone | N/A | Pokégear instruction booklet trap | Rhydon trap | Special (location) | This Game Pak is designed only for use on the Game Boy Color. | This Pokémon cannot be traded.
?????????? | ????? | ! | Abnormal Pokémon | Bad Egg | Enigma Berry (Generation III) | Error! | Error codes (Generations I and II) | Error traps for damaged save data | Error traps to prevent impossible progress | Event data debugging messages | Instant victory effect (Generation II) | Mystery Zone | N/A | Pokégear instruction booklet trap | Rhydon trap | Special (location) | This Game Pak is designed only for use on the Game Boy Color. | This Pokémon cannot be traded.
'ERROR!' is an unused option string that can be forced on an options box for the party Pokémon screen. Its purpose if anything is undocumented.
It follows on from 'MAIL' (hex:14); the last valid option. Field moves have index numbers between hex:01-0E, so "ERROR!" probably wasn't supposed to be one.
GameShark code
Enter the GameShark code 0115D6D0 to replace the third party menu option with "ERROR!". All ERROR! does with this code is function like cancel.