Darthunder an Phoenix: I got an answer from Eric (3dscifi forums) today. Here it goes:
My best guess, since I don't see any restrictions on those images, is that they should clear their cache in their web browsers and reload the page they are trying to view.
The only other thing I can think of is for them to try to access the images from a different location. If their ISP is blacklisted by one of my spam lists or something, then that might prevent them from seeing images, but I'm really reaching here. If this was really the case, they shouldn't even be able to log on at all.
Let me know if they have better luck after clearing their cache and reloading the page. What browser are they using? What OS are they using, do you know?
Eric is an admin (nick scifieric), and you can contact him if the trouble persists. ;)