I would think this as well, except that when I didn't know what was going on at the beginning of when this problem was occurring, I would turn all external processes off and then back on again intermittently for 10-20 minutes (not changing anything within mixbus) and it would successfully export.  I would then try to export again (changing nothing anywhere), and it would fail completely to export at all.

Very frustrating.  I've been working on this off and on now for months.  You guys are the first people to actually respond.  It seems like I'm the only person on earth having this issue.

Thank you for looking into this (or at least giving it a bit of thought).

--Jason