I am having this same EXACT problem. Experimenting, I exported to AVI, generated mono file per track, and rendered uncompressed - I ended up with a viewable file, but it was weird. It was a split screen, split vertically, showing the video in both screens, and there was no sound.
I would love to use Lightworks for editing, but until some of these issues get settled, I'm forced to use something else while I wait. I will be eagerly waiting and checking back often.