iPhoto help please, some pics are 'missing'

I'm viewing my album, but about half of the pics are either showing up as a grey and black ! mark. if I try to view them in edit mode, there's just an empty icon that looks like a place holder. I can see all of the pics if they're minimized, but if I click on them, the frustration begins.

did I mess up a setting?

Did you do anything to your photos from within the library in finder? Rename, reorder, etc.? That will surely corrupt your iPhoto library.

You might try the rebuild function. Directions are on Apple's Knoweldge Based support site.