I found today interesting problem and I must confess, that I don’t know how to solve it. You have a lot of feed types in WordPress. One feed - http://vitamin.seopeter.com/feed/ - show the header 404 Page not found. It shows some XML, but if you have not any posts, than WordPress shows it as fault.
So I had to add some post. This post. And now it is all OK. I just hate WordPress sometimes.