Lightbox hides at the bottom of page

Hi, folks! I'm using Simple Lightbox 2.0RC4. The lightbox hides at the bottom of the page, so I have to use de scrollbar to find it. I've tried with some others pluging (including jQuery Lightbox For Native Galleries), but all with the same issue. It used to work pretty well. I don't know when this issue began. http://www.colormixstore.com.br/site/?p=3077