Popular Posts Not Displaying

Hello – I just installed the plugin. Trying to get it to display just my most popular posts but it’s blank. It shows the widget title (which I’ve set to “Popular Posts”), but no posts display underneath. When I select the tab “recent posts” in the widget settings, then it displays my most recent posts, but I want it to display the most popular or viewed. Am I missing a setting? My site is http://paleodulce.com/. Thanks for any help.