I have been getting that issue with people I can connect with lately.
But as for everyone else, I am still getting the same error message, namely Error Code 86420, which refers to a firewall issue on the Nintendo site. I have disabled all of my firewalls, followed the instructions on the Nintendo site, called them, and they were unable to resolve the issue. I'm curious as to why this error occurs for majority of the people while a few others can connect with me fine.