Lightbox for single images

Hi, I haven’t had any luck using a lightbox with single images. I tried deactivating plug-ins with potential conflicts, various compatible lightbox options, but still isn’t working. Any ideas what could be causing it?

I’m encountering the problem on a few places on my website, but here’s a specific example:
http://www.sawillis.com/?royal_portfolio=yeti-cooler

password is: opusopus

Thanks!