Each post that has a gallery - if you click on any image in the gallery, when it attempts the Lightbox transition (hope that's the right terminology), the screen dims and rather than a larger image appearing, I get a broken link icon and the word 'undefined.' The left and right arrows don't work, and clicking anywhere else on screen doesn't return to the post. I have to use the browser's 'back' button to get it to respond.
I updated the theme, am running the most recent version of WP, have disabled all my plug-ins, tried a different browser, and still no dice. When I attempt to edit a post with a gallery, sometimes the gallery icon (the large blueish box), shrinks to a clear 20x20px box instead.
Any help/advice would be appreciated. I'm at wit's end. This all worked fine last week and the only change was scheduled posts posting over the weekend.