[Plugin: UW CALS Extend RSS2 feed] Doesn't work

Hi!

I installed the plugin, activated it, have custom “thumbnail” fields for all my photos, typed in the URL for the feed using the URL extension /?post_thumbnail=1 and the photos don’t show up. Interestingly, there are no thumbnails on the UW CALS website either. What am I missing? I’m using WordPress 3.2.1

http://wordpress.org/extend/plugins/uw-cals-extend-rss2-feed/