What to do:
If the Wii U Nintendo eShop service is undergoing maintenance, you will receive this error code when attempting to perform a system update. Click here to view our Network Status page.
Wireless interference between your Wii U and wireless router may be causing the download to time-out.
As an easy solution, try moving the Wii U into the same room as your wireless router during the update, and then moving the Wii U back once the update is complete.
If you are unable to do this, try our more extensive wireless interference troubleshooting. [How to]
Entering your network information into the Wii U my improve your connection with your network and allow the update to complete. [How to]
Still Not Resolved: