Unfortunately, that comment box is not available anymore. The comment box which allowed anonymous comments was deprecated over a year ago. If it was in use on your site before that time, Facebook still allows its use, but there's no way to use that now on a new page of your site.
There are options to allow users to post (using the new box) with other social sites that weren't available in the old box, but unfortunately, there's no way to do anonymous posting with the new boxes.
Hope that helps explain, and sorry it's not the answer you were looking for.
Alex
How can I allow anonymous comments (no need to FB log-in)?
