Why do my video files from my Flip Video only play the audio when exported from iMovie?

I am making a video from a Flip Video Ultra, intended to be used on youtube and an eCommerce website. I imported the .AVI files directly from the camera into iMovie ‘08. The video plays in iMovie and the .AVI files play in Quicktime. As soon as I export them to the .m4v the video is gone (black screen) and only the audio remains. (in both QuickTime and iTunes) I have made no edits as of yet. Just wanted to share the initial file, but it doesn’t appear to me that it will be any different when I am done editing…

I also tried copying the files to my desktop first and importing from there. Same problem.

Is there something I am doing wrong, or something I should know? (I’m pretty new to video editing.)

Yesterday I was able to make a “movie” of images with an audio track. That process went very well and was exported to youtube with no trouble at all. And the m4v file plays as one would expect.