There is a bug with the plugin. After many hours trying to figure it out i was able to successfully make the images load. What you will need to do is create the gallery but NOT upload any images to it and save the gallery. Then go back to the gallery and upload the images and they will work.
Now that this works i would like to point out that adding multiple galleries to for example a photo page does not work properly. The thumbnails created for each of the galleries appear to be scrambled all over the page. I had to manually create images for each gallery category and then manually add them and link them to the gallery pages.
Hope this helps. Overall this is a great plugin.