Also – the name of the gallery no longer appears. It just says above the thumbnail images – [show slideshow]
I created a new gallery and got the same 404 error page after clicking on “Sort Gallery”.
You also get the 404 error page if you try to delete an image in a gallery or try any of the other options that appear in the drop down menu within the NextGen manage gallery options as seen in the attached screen grab. All you can do is add images to a gallery and nothing more.