Since it happened while just reading your memory, the chances of that breaking your system is pretty small. If you were writing the NAND, then you would have been in trouble.
I would back up the NAND files (keys.bin, since nand.bin is 0bytes, it's garbage), delete the two files, and then just try it again. You should be able to put the SD card back in the system, and it should boot directly to bootmii since you've installed it as boot2. Then, try it again.
If it still locks up, then you may want to try a different card, keeping it to a 1gig or 2gig card.