The following information comes straight from a Nintendo customer service rep. There be some spoilers involved, so I've split the details into two sections. The main spoilers come after the jump.

We have been made aware a the issue that results in being unable t' progress in the Song a the Hero quest. If the game has been saved after completing the sequence a events, it will no longer be possible t' proceed through the game on that save file. The only options at that point be t' either start the game over or t' use an earlier save file t' continue.

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