I have the same problem as mentioned in the OP. I changed the var code as described here, but I get very different results in each browser.
Google Chrome : works fine
Opera : the "Close" buttton displays, but with a "null" written in the bottom-left corner. Additional problem : the zoom function doesn't work and makes the photo blink on mouseover.
Internet Explorer : "Close" button doesn't display (red cross) AND the same "null" word as in Opera shows up.
Firefox : "Close" button doesn't show at all. No red cross. The white space under the photo is too small. When clicking where it should be it does close the lightbox, but visitors would never guess.