you probably get some form of warning when you try to "view" a picture by double clicking on it.
I recently reformatted my macbook (feeling regretful now) and after migrating my "iphoto library" file from external onto my macbook only certain photos will be viewable when I click on them. In addition, I cannot "preview" any when scrolling through events. I have iphoto 11 and am running Lion. PLEASE HELP!!!!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic