I don't know if you have already solved the problem, but I found the same thing... it was like the title mask was inverted and painting all of my video black.  Only the title's wording was showing the video below it.  However, exporting in QuickTime or any other format did not quite fix it for me.

I noticed that the software had an update (go to the Help tab then Update Online option).  Once that was installed, everything is exporting correctly.

Hope it helps!