iMovie '09 Doesn't see some of my iPhoto movies

I took digital movies with my iPhone. I imported them into iPhoto. Now, when I go to iMovie, it sees only SOME of the recently imported movies from iPhoto, but not all of them. ??? Why??? How do I find these missing movie clips??? They are on iPhoto - I have double, triple checked, but when I click on the "photo" button on iMovie, only some of them show up.