After doing the fix for the infamous 018-0512, all was right with the world until yesterday.
I help send Swapnotes on a few forums, and had added a few people to my friend list. When checking to see if they added me back, I got this error.
Weird part - Swapnote worked. The Internet browser worked. Netflix worked. ANimal Crossing worked.
Just my friend list seemed to trigger this. Resetting the router fixed it, but it returned again today. Everything works except appearing online.