Well with the first person in that topic it was a permissions issue with files of the theme on their server. But on with the second person I’m not sure yet.
On your site, it’s happening with WordPress’s default theme, though. Your specific problem doesn’t relate to the Complexity theme in any way (where as the first person in that other topic could narrow it down to files of the theme). It’s something with your WP installation. But I searched around on the wordpress.org forums, and tons of people are having similar problems it looks like with no real clear answer on how to resolve.