Getting no popup

I installed this great plugin on this page http://mozdren1.com/mozuser2/home/
in the left sidebar, and when I click on the button, I don’t get the popup, just a transparent overlay. Any reason why? I really need this to work for this website. It is the perfect solution for my friend to use. Thanks.

http://wordpress.org/extend/plugins/wp-tell-a-friend-popup-form/