Ok, so I checked my SD card, and it's perfectly fine. The 3ds booted with the SD card, and sometimes booted with the flashcard inserted. The flashcard is a R4i Gold 3ds (One of the first two supported by ntrboot) It seems to work fine on my other two 3ds consoles. And I tried to restore the nand backup that fastboot3ds made in godmode9, where it told me "No nand FIRM. Nand backup file is corrupt." I had one from earlier, as I said before, that worked fine. I have since reinstalled fastboot3ds, along with the system firmware to 11.6, and it continues to work fine.