Thankfully, this warning like many others is normal for login problems (Source)
Official Blizzard Quote:
The Diablo III servers are sometimes taken offline in order to resolve critical issues. While we try to keep these occurrences and their duration to a minimum, maintenance is periodically required to fix issues that would otherwise negatively affect your gameplay experience. The following error codes typically indicate that the Diablo III servers are offline:
If you receive one of these error codes, we first recommend checking the Diablo III Technical Support Forums to see if other players are experiencing the same issue. If you see many posts about your error code, it is likely that our servers are temporarily down for maintenance or are being restarted. We appreciate your patience, and we'll have the servers back up and running as quickly as possible.
For me, when i got this error. It was after mega spamming login this morning. There may be a limit on connection attempts either from certain IP addresses or within your home router. Reboot your router, this fixed the issue for me.