Can anyone tell me what imovie error -108 is?

I was trying to publish a project to YouTube and got this error. I have over 50 gb on my hard drive and the movie is HD, about 4 minutes with quite a bit of editing involved. I also tried to export it directly to the hard drive with no luck. I'm using iMovie '09. Thanks for your help!

Zach Green

youtube = zachisthname