It'll be easiest just to describe my situation... I have a "Photo Album" page at http://www.tracyandcarol.com/the_tracy_times/photo-album/. Currently it has 2 gallery listed on it. The galleries are linked to pages that are marked as "private pages". When you click on the thumbnail to see the gallery you get a "Page Not Found", though the url is correct in the address bar.
This doesn't happen 100% of the time, but happens over 1/2 of the time.