I don't think this plugin is working with WordPress 3.5.
If images were uploaded and inserted into posts PRIOR to the WP upgrade, they still open in a lightbox...but new images have a problem. It seems like that when this plugin is activated in WordPress 3.5, it prevents the "link URL" field from "sticking". I link to the file, save...but it doesn't open in a lightbox. When I check the image link, it has been erased from image.
I love this plugin! Any chance it will be updated for 3.5?