This no image box thing was happening to my wife last night in several skin libraries. Page refresh didn't fix it, but if she went from the libraries to the forums and back again, the missing previews would sometimes reappear, sometimes not.
Thing is (two PC's), I could be on the same gallery page and the missing previews on hers would be present on mine. Dunno if her not being a subscriber as yet has any bearing (wouldn't think so), but she was logged in and the issue, as others have stated, was not confined to any specific page but was intermittant/random.