iPhoto problem

When using iPhoto, I select a picture I want to enlarge, I couble click it and the screen shows a large exclamation mark in black.What causes this and how do I prevent it ? Thanks for any help. Van

I'll bet you have done some organizing/editing of the iPhoto library file in finder, haven't you? That would cause the problem you are seeing. Users are not meant to be accessing those files, we need to do anything and everything to/with our photos from within the app itself.

Now, to correct the problem, you may have some luck doing a rebuild as described here: iPhoto 6 and later: Rebuilding the iPhoto library.

If that does not work, you may have to reimport all your photos.