I'm not too experienced with NextGEN Gallery, but I have a client site with a slideshow that stopped loading images at some point, so I'm troubleshooting. I think I can trace the problem to a request like this:
Gallery ID 2 has 13 images in the admin, but the response to the above request is empty:
<playlist version="1"> <title/> <trackList> </trackList> </playlist>
I'm not sure when this started, but I tried upgrading from NGG 1.7.2 to 1.7.3 without any effect.