I was running into this issue and most of the help I found on the internet was either too time consuming or didn't work. In this case, I eventually found the answer on an apple forum. In the past I've had bad luck finding such information later on so I figure'd I'd save it off on my small corner of the web.
Here are the symptoms I was experiencing:
- I had recorded a video with a different piece of software and imported to iMovie
- I added voice over & edited the video and all seemed well
- Went to export to a file and immediately it throws the error 10004 before the pie starts to fill up at all
Thanks to Bruno's review I was able to easily resolve the issue. If only that were the first advice that I'd seen....
Anyhow, just delete the first second of the video clip and add a freeze frame if necessary to make up for it.
Then exporting works fine for me. Hooray!