It is nothing to do with the lightbox mod. Try switching off javascript on your browser and then click on the bottom right image. It isn't the same image as in the picture.

Basically the lightbox is looking for an image in images/large/fac... but no such image exists, so the lightbox hangs. Try copying your large image to "http://starruby.in/store/images/large/Faceted-Rubies/2.32-carat-oval_001_LRG.jpg"