After hours of post reading this "QuickTime Error 0", I found the solution by going through the time-line very carefully and coping and pasting portions of my project into another time-line and exporting out as ref QT's till the error popped up, and I honed in on and isolated the clip that QT didn't like to render, replaced it with dragging the same shot in, and re-rendering and BAM! 100% rendered and exported. If you have the time, it's worth the fix, but if not, not sure what other options there are. The only other solution I found before was to output to an SD QT, rather than keep it at same settings or exporting to an 8-bit. All exports failed except for the SD 720x486(16x9)QT export using QT, not QT conversion. Then I tried this isolating the corrupted clip idea, and it worked. It was one little tiny 4 second cutaway shot in my 12 minute clip.
I found these 2 posts to help me in that direction: