No Images Showing in Gallery Builder

Hello,

I recently installed Responsive Lightbox onto my site, but I haven’t been able to use it yet because I am not able to select any images in the gallery builder. I have a large media library but no images display in that or any of the other tabs. Please see the attached screenshot: https://webpagefx.mangoapps.com/sf/MzgxOTc3Xzc2MjU5MDc

Any help you could give would be much appreciated!

Thanks