I think there might be a bug with the choice of language. If you use another language than english (swedish for instance), the plugin will show the text in spanish.
A future request would be to include a language picker in the options page.
I’ve been wrestling with this problems for days, trying all the suggested fixes. For me it turns out it’s a plugin that is breaking the visual editor, Dagon Design Sitemap Generator. It seem to be something wrong with the language settings which causes a header error.
