After upgrading to Snow Leopard and ILife, whenever I try to delete older photos from IPhoto I get a grayed out square (kind of like a placeholder) and sometimes IPhoto will freeze up and I must do a Force Quit. I have rebuilt the thumbnails as recommended, etc several times with no luck. Any suggestions?
— Joyce Wells
I sounds like your library may be in bad shape. So you tried the technique here: http://support.apple.com/kb/HT2638
-- I'd do all of the options, not just rebuilding the thumbnails.