I'm pretty sure it's the bozos at Netflix. I have 3 AppleTV 3s that can't login. Same error and no results with search on their site. Netflix wasted an hour of my time between two chat technicians. I kept asking if someone threw a switch too soon because they sent an email out saying after July 31st the device isn't supported.
Tried unplugging the Apple TVs. Changing the password on netflix. Restarting the router. Logging in on the web (worked fine)
We ended up at doing a speed test from the laptop I was on. 6.7Mbps. Should be faster but no matter. I can watch Amazon and Apple streaming movies fine on the same devices with no buffering. I told them I can watch movies on my iPhone or Laptop using Netflix right now.
Netflix solution after they said they ran through all troubleshooting steps? I was told that 6.7Mbps is way too slow and I need to upgrade my Internet service to a faster service in order to be able to log back in. I asked why I could stream other services on it and I was told the Apple TV needs more than 6.7Mbps just to login. So, contact my ISP about the problem.
At this point I just closed the chat window. They still cannot login today. ATV-ui93.