Here is a list of all known error codes to EndlessWFC and what they mean:
23000 - Console registered - if getting this error more than once it might mean that manual activation is enabled. Please contact us to be sure.
23800 - Game not supported by EndlessWFC - EndlessWFC only support Mario Kart Wii and Mario Kart DS. This error may also be caused if your game ID is improperly set.
23913 - Console creation denied!
23914 - Console is banned!
23915 - Attemtpting to tamper with console identifiers