Hi Andrew,
Did you have any luck finding a solution to this problem? I’m having the same problem (machine specs are almost identical to yours) which is occurring across all projects, so it’s not a media issue – exporting to any other codec is without issue; only h264 produces the error message.
As you say, it’s more of an incovenience in the workaround rather than a massive problem, but it would still be great to know why it’s happening and hopefully fix it.
Thanks,
Kyra