I also posted the same question on the Rockbox tech forums. The reply was to boot the fallback image and try again. I did that, but got the same error. Then I formatted the data partition again using EmCore's menu, and managed to mount the partition. But there was an I/O Error on the drive (I confirmed that on the terminal). So it seems the HDD is busted. Time to change to another player.
5/19/14 at 12:57am