I previously used Jalbum
to create my online galleries. When I found minishowcase I immediately converted, due to its ease of use.
When I installed MSC I just moved the images that Jalbum had already resized for me into the galleries directory and everything worked great.
Then I uploaded some .JPG's from my camera. MSC can see the gallery, it can see the images. It knows how many there are and puts them in the appropriate gallery. However, it does not create any thumbnails for them, or show them in the preview. When you view the full size image, it works.
So after some experimentation I've decided that Jalbum does something to the images. I created a test gallery here
If you look at the Test Gallery you can see one image processed by Jalbum and one that hasn't been. One works and one doesn't.
I am fresh out of ideas. The latest set of pictures I uploaded would not work at all no matter what I checked, until I created an album with Jalbum and uploaded its images.
The full album is here