I'm having the same problem right now. I have a paid for version and cannot export my video project. It's weird. Everything looks fine when I preview my project through the Sequence preview, but nothing shows up in the Project Preview or exported file aside from 2 seconds of a black screen. I spent all this time editing a surprise get well video for my husband, and now I can't show it to him.
PLEASE HELP ASAP!
Thanks,
Mads