I had the same problem. The gallery stopped working. It occurred that I had no “<?php wp_head(); ?>” in the header.php. Check your template. Hope this will help you.
Try to upload your images once and then go to Add Gallery/Images > Import Image Folder to choose the one with images. If you see info that 0 images has been uploaded add “/” each time, eg. “/wp-content/gallery/slides”, “//wp-content/gallery/slides”, “///wp-content/gallery/slides”. This solution uses a bug, but works great.
