TCaC04, I finally found out the problem regarding the hard drive. It apparently has a sleep function, which makes the drive go to sleep after about 10 minutes. I doesn't wake up until after I restart the Wii U, so this is why I can't save my games after 10 minutes.
Bummer. There's no way to turn it off at all? If not, that is a real disappoint. Check Amazon and/or Newegg for good deals on HDDs.
Not sure yet. My dad and I did some research on it about the problem. We found this thread: http://forums.toshiba.com/t5/General-Features/Canvio-sleep-function/td-p/347620
Paper Mario: The Thousand-Year Door Quiz-Master Badge From Chaosmaster00's Paper Mario: The Thousand-Year Door Quiz (January 2008)