Hello, I have encountered a bug in NextGen 1.9.6 when image filenames contain spaces, and possibly apostrophes. I had some image filenames that looked like this:
"Foo'Bar 2012 001.JPG"
Thumbnails for these images would not appear in the nggallery-manage-gallery administration page, and if I click on the image name, I get a 404 error:
The requested URL /wp-content/gallery/2012/Foo'Bar2012001.JPG was not found on this server.
NextGen appears to be stripping out the spaces instead of url-encoding the filename for the link.
I renamed my files, taking out the spaces and the apostrophe, and after that it worked properly. I did not do an isolated test to see if the presence of an apostrophe had anything to do with it.