Hi, I'm new to Wii U. 
I am unable to register a friend's Nintendo Network ID on my Wii U system via Friend List or Miiverse. All other internet related tasks work just fine - I can browse Miiverse and the web, download updates and use online features in video games. In Miiverse, we're able to follow each other and see the other's posts, but when I try to request him as a friend, the "Send Friend Request to [friend's name]" turns really pale for a few minutes before giving me the following message: "Error Code: 121-9998 Could not connect to the Internet. Please check your network connection and try again."
When trying to add my friend in Friend list, I get the message "Could not find the ID you entered. Please check that the ID is correct." I'm sure it is, since we are following each other.
I'm at a loss here. Everything works wonderfully except this crucial bit - friend requests. Does anyone else have any insight as to how this could be fixed?
TLDR: Wii U works great. Console is online and all online features work except adding friends.