Thumbnails not displaying images

I have regenerated all my thumbnails with the plugin “Regenerate Thumbnails” but still cannot get images to display with my YAARP thumbnails — instead, post titles and links are paired with what I assume is the default image box of diagonal gray and white stripes. I’d really like to use this plugin but just can’t seem to get it to work. Any tips?

http://wordpress.org/plugins/yet-another-related-posts-plugin/