Nevermind, I found them in vsel_shortcode.php
Well, ultimately I had to ditch this plugin. Despite what I said in my last post, the “Sorry, there was an error loading next page” keeps showing up with no apparent rhyme or reason. Shame too, it’s a nice plugin when it works as it should.
It appears this is a temporary inconvenience. The two problem pages that I linked to above are now working, so I added the gallery code to a new page and that page is throwing the same error.
I can only assume that this has something to do with the API and takes some time to start working properly on each page I add the gallery to?