Since there is no LucasArts key registry, I am going to try to see if this works https://www.gog.com/forum/star_wars_battlefront_ii/fix_for_your_cd_key_is_not_authorized_found

My friends and I were looking to play again after so many years, one person seemed able to join a game, but the next person gets the 'CD Key not valid' error when trying to join. We just downloaded the game off of steam and replaced the files with the gamespy 'patch'. Any help would be appreciated!