Lightbox problems

I am helping a friend with her WordPress site, and she has Shashin installed using PrettyPhoto. When we click on the photo to enlarge the thumbnail, the screen goes dark and the enlarged image scrolls behind the content and navigation.

http://www.pinuppoleshow.com/photos

Here is an example. Is this an easy fix, maybe something I’m missing, or is it a theme/script issue? Any help would be greatly appreciated!

https://wordpress.org/plugins/shashin/