Two Picture Windows Opening

Hello,

My products all have two windows opening when you click them, here is an example:

http://wip.dvmobiweb.com.s181553.gridserver.com/product/superluxe-mat

I have a product image set on this one, and nothing else. On others I have a product and gallery image, it does this on all of them. How can I get only one window to pop up when users click the picture?

Thanks!