You're not supposed to decrypt the update files... You're only supposed to download them and place just the files, not the folder, onto your SD card inside of an /install/ folder.i have the same problem, Downloaded with NewNusgrabber, use decrypt and wiiu key, placed the downloaded files ( all of them) in install folder and boom install ok... freeze Martio kart 8 ( 5.3.2E) downloaded EUR NUS
And if you're on 5.4, then you need to use the other version of WUPinstaller I posted here.