It could be that I updated a few plug-ins (although I have done it before), but jquery-lightbox plug-in had suddenly stopped working. All galleries had gone from nice to just sending me to image in the blog post?! or in the tab, when I click on image. The link goes directly to the image file. I have also updated WP to V3.6.1 recently
Every listing has a gallery. I found jQuery Lightbox very convenient and simple. It worked well until now. I haven't made any changes in the code and all plug-ins are pretty much the same as they were for quite some time. I checked header.php and footer.php to make sure that everything is OK there, after reading these lines :
Make sure your theme calls wp_head() and wp_footer() correctly.
In one of the forums people attributed malfunction of jQuery Lightbox to WP recent migration?!?! Something about image links directed to the old ... whatever... servers or something.