Might be your sd card.
Are you letting the hackmii installer format your card before trying to install it?
It not next time let it format it.
Also it might be the kind of card your using.Bootmii is picky about the sd cards.Make sure its a full size sd card and not a mini or micro sd card.
Also its pointless to make a nand backup if you have it installed as an ios because even though it allows you to make a backup it will not allow you to restore it.