If you take the music off does the video run through properly? If so I suggest you make the movie with the voice over then import it and edit it with the music you want. I have found several times that if you try to do all you want in one go problems often occur. I often make short clips and then join them which I find helps processing as well.
You may also find some help at the Pinnacle Forums click here and in the FAQs click here.
Whether the e-mail support would be willing to provide further help I doubt, but it may be worth a try.