I had this problem, too, but it was because I had set all my images to "display: block" via my main CSS file. Changing the images to "display: inline" in the lightbox.css file should fix it.
Deathpie, thanks for the heads up. Display:inline didn't work if I had that in my Lightbox.css file, but as soon as I got rid of the display:block in my main CSS file, everything was good. Thanks again!
dcdomain, could you be a little bit more specific? since i can't find exactly what i have to do. Or which one of the "Display:block"s to modificate/delete.