iMovie uploads

I love to use iMovie to make videos for my son's baseball team. I gave myself a heart attack because when I went to upload the clips from the last view games, none of them showed up on the import screen. I thought my disc/card was corrupt. But I went to dropbox and uploaded. The clips are there. For some reason iMovie is not recognizing them. I haven't changed anything in my process or how I record on my video camera. Does anyone have an idea on why now iMovie isn't seeing them to import?