Load bootmii and make a new nand backup.
Take the new nand.bin backup made from bootmii and format it with giantpune's nand.bin formater, "Ohneswanzeneger".
Format the nand.bin
Then install system menu 4.1u from "Ohneswanzeneger", set your setting.txt to the proper serial number when you do this.
After that check your nand.bin with giantpune's nandbincheck, make sure there are no errors.
After that restore your new nand.bin using bootmii's restore. That should fix any issue with your wii's nand system.
nandbincheck nand.bin -all -v