I bought a Wii-u yesterday, and I started the giant system update around 6pm..
After almost two hours it got an error code while downloading data for the update (maybe at 60 percent by then) So obviously we tried again. A few more error codes and hours later, it finally went to the actual download of the update. it easily climbs to 99%... then another error... After reading up on this, we moved the Wii right next to the router and tried again. I also tried the changing all the connestion settings manually thing.. After hours and hours of errors that never got past the data download part of the update, we gave up and played a game for a little while, then headed to bed and left the system on, updating while we slept.
Wake up now, and there's no update.. not sure what happened.. We're trying it again now.. but it's been about an hour and there's barely a dent in the data download..
I don't know what to do aside from calling nintendo. I've tried EVERY tip I could find on the internet and nothing worked..