Solved -- nothing wrong with script (or next() function)... by viewing generated source I spotted a couple of egregious markup errors (fail)

Hmm, well, not quite it seems. Though fixing the errors got the thumbs working at least on the first instance, the pPopup is doing some weird stuff to the generated code (moving the .pop divs to the end of the page hwere next() can't find them for repeat clicks. Damn.

It'll probably be moving the div to the very last element on the page so it can make sure it appears above all other elements on the page.

If that's the case, you'll probably have to be a bit cleverer with the div it is moving, have only 1 for all the thumbs and dynamically change it's content depending on the thumb that was clicked.

I thought z-index took care of that, but I have a poor understanding of how the popup works. I've suggested to the author that instead of moving the popup div, he copies and (on close) destroys the copy, leaving the page in its original state, so we'll see if that's viable.

The problem with z-index is that it is relative. By moving the div so it's a child of the body tag, it will have a relative z-index to elements that are also children of the body tag and not of the body tag's siblings' children.

See http://stackoverflow.com/a/7482870 for a good explanation.

I managed to get it working by overrridng the bPopup "append" function (with a handy parameter), and using JQuery clone() and remove().