MC 6.03 and MC 5.5 black frames.

I am getting seemingly random black frames on playback, but on only one of my systems. my older Mac Pro plays the footage fine.

I have two systems: Both are Intel MacPros, System 1 has. OSX 10.8.5. Media Composer 6.03. Using a Matrox mini. System 2 has OSX 10.6 and Media Composer 5.5. and no external video card.

I have random footage that plays back with black frames at irregular intervals. a black flashing of 1 or 2 frames. The black frames do not seem to move around.

Footage is 5k REDRAW transcoded with Resolve to DNX 36 8 bit MXF. Not all the footage from the same batch has this problem. I have turned off the Matrox card in AVID, but still have the problem.

Any suggestions as to what to look for. I've never had a problem with so few references (none) I could find on the web.

Preliminary research is pointing to black frames where created in resolve when a drive was too slow. There may have been replacements made of the dailies that had not been copied to both systems.