I assume that you are using some software to download the pictures from the camera.
If so, the problem is likely the software.
I suggest you use a card reader attached to your computer.
Then you can see all the files on the card and download them.
Or you can take the card to your local photo printing store and have them copy the photo files from the card and burn them to a CD.
I have 100 pics that are visible only from the camera but when I'm trying to download in the PC the camera looks like they have no pics in it.
If I make new ones then I can see and download these new pics only but the one that are hidden I can't.
Any idea and suggestions?
Otherwise I have to erased permanently from my card to free the space.