I know this is old, but since this was one of the few messages that came up when I did a web search for this error, I wanted to add the solution in my environment when I got this error.
It turns out through a bizarre sequence of events, I had lost all my DNS servers. Once I got that issue fixed and rebooted my NSX Manager, it came back up fine. This was a lab environment, so I only had one NSX Manager Node.
