Sorry to hear, beating the Pink Flower challenge was one my favorite accomplishments on Pikmin2 and the Gamecube.  

Don't know of any fixes myself but am just curious if it was a 3rd party card or if it was used on the Wii? 

I had a large 3rd party card get corrupted from just saving on Resident Evil 4 and hear that the Wii too can sometimes corrupt..

Take both cards out of the GC, dust inside the memory card ports with a Q-tip (cotton bud) also try and dust the contacts for the memory cards, insert them one at a time, just test them in the GCs main GUI, not inside a game, if you get a message that asks you to format the cards just take it back out, try another dusting, blow into the ports of both the GC memory card slots or into the contacts on the memory card isn't a great idea since vapour from your breath will go on the contacts and can corrode them.... but it's always worth trying out, but yeah go for it through the GC's main interface not inside some game, 1 card at a time, try both ports on the console too, might be something up with the system so just double check in slot 2.

Good luck man, hate losing data from older games, I know you always keep the memories of doing them, but losing saves is always harsh.

I can approve this. When I got my Wii I copied the gamecube memorycard with it and it corrupted some Savegames. I was angry for a short time, but than I decided to concentrate on new games instead of living in the past.

And the New Play Edition of Pikmin 2 for the Wii is better anyway.

Yep they were used on Wii. It would be really shitty if that was the cause.

You should tag Metroid Prime 3: Corruption in the thread title. It won't help your plight but it would make me smile.

Game Shark (Or Action Replay). You're welcome.

One reason I keep my Wii. It's hacked, so I can backup the GC save files, along with Wii Saves. So even if it happens I restore them. It's hard to do, if you're not comfortable with it. But it's the best backup. I'd just replay the games, in your case. Gives a reason to play again.

Come on! Unlocking everything in Melee once again won't take too long!

Happened to me with a PS2 memory card. 5 years worth of gaming, all deleted with a push of a button. I guess I just had to deal with it and remember that I will never forget about all the gaming achievements I did and the games I finished throughout those 5 years.

I noticed it happening when they were in my wii. Not the 56 or 128. But anything bigger seemed to randomly corrupt now and then