The problem has been reported on numerous boards. Try these steps to fix the problem:
-Make sure you have NO Easy difficulty saves on the memory card. This is the number one suspected cause, as NO ONE has gotten it to work with an Easy difficulty save. If an Easy save is the only one you have, you may be out of luck and need to go back and play Path of Radiance on Normal or higher.
-Make sure you're using "cleared" data. If you haven't finished the game, you can't transfer.
-Try doing it a few times. Some people have reported that it does work after they started resetting the game multiple times.
Nintendo is aware of the problem, and they are working on it. From what I've gathered, they might distribute a fix through a future update. If not, the only thing they could do is have some sort of disc replacement once they come out with a fixed version of the game. It is almost certainly a programming issue. Just be patient.