I know that there are many guides on here for this. I read them all and tried many things. I kept getting error 0x00000000 and many of the recommended nus downloaders didn't work for me either. I'm just going to share how I got it working for others in the same boat as I was. I take no credit for any of this. This is pieced together from multiple gbatemp contributors. Here's the steps I used on my 5.4 spoofed to 5.5.1 First things first. Make sure that all auto-shutdown and sleep modes are turned off on your wii U. You don't want it to shut down in the middle of an update! 1. Install on a PC this: new-nusgrabbergui https://gbatemp.net/threads/download-the-new-nusgrabbergui.411228/ 2. After opening new-nusgrabbergui (you may need to get the latest c++ redistributable first) click on "Update VersionList". This will take a bit. 3. Search for your game. 4. Select your game from the list and make sure that "Latest" is highlighted under "Version:" 5. Click Download and then go grab a bagel and some coffee. (could take a while) 6. When it finishes you will have a new folder inside of your new-nusgrabbergui folder that starts with "000.." 7. Copy everything inside of that folder to the "install" folder on the root of your wii u SD card. 8. Run locally hosted non loadiine kernel through xampp. (There are many ways to run the kernel exploit. The WUP Installer itself has one build into it but I could never get that one to load very well. You can also use online sites if that's what works for you. I'm only sharing what worked for me). You don't actually have to run WUP Installer twice contrary to what many will say on here. You only need to load it more that once if you haven't already ran the kexploit successfully. 9. Run locally hosted WUP Installer through xampp. I tried many different builds and this is the one that worked for me: http://gbatemp.net/threads/wup-inst...fing-5-3-2-5-4-0.397053/page-123#post-6080452 thanks @skalienx! 10. After launching WUP Installer Hit the home button. Instant Freeze! 11. Let sit for about a half hour (500MB install). The general concensus is that you want to wait about 15 min for every 250MB so for a full gig would be a full hour wait. 12. Hard reset. The data is there!