Weird iMovie glitch

I've been importing video from my old digital camera onto iMovie, (have about 65 hours of video) to later edit, and am putting completed movies into an external hard drive. All has been well. But today, after importing some video, iMovie didn't produce thumbnails at all, even though it said it was. So I am stuck..it's been working great for the last 8 videos, now all of a sudden it won't produce thumbnails on this last video, so i can't save the video. Anybody heard of this, and what can I do????? Help! I'm getting paid for this project, so I want to do it right...thanks! Oh, and if you have the time, you can email me at; nico.dagger@hotmail.com thanks again!