Pokemon Colosseum and XD are very picky about their save files, and using save states can mess it up. Usually happens if you take a save state, save in-game, and then reload your save state and try to save again.
I'm pretty sure you have no other choice except to load up your last in-game save to get your save file working again.
I'm pretty sure you have no other choice except to load up your last in-game save to get your save file working again.