Well, the image on that page is
http://cfferns.com/wp-content/uploads/wpsc/product_images/Rabbit Foot (White) - Humata tyermannii 2.jpg
I suspect the problem with your lightbox is either the forward slash in your rel attribute, or possibly the spaces in the path to the image:
/Rabbit Foot (White) - Humata tyermannii 2.jpg" class="thickbox preview_link"
If you look at the console for your page you'll see it's choking on the rel attribute, so I'd start with that.