I had that for about 2h yesterday. That's the generic server page you get when your webserver is working, but has no documents to serve out. Site must have had a failure at that time. Kinda like the test pattern you used to see on TV late at night.
I also got 404 error pages for a while.
Yes something was going on yesterday.... our host company was installing an SSL certificate (security stuff) in anticipation of a new feature we will release in the upcoming weeks.
Sorry about all the trouble. As always, working hard to give an awesome experience on the forum and improve things.