Your intermittent problem may have to do with the logging feature. I encountered the same problem today while trying to export two simple graphs from the same sheet as PNG files.
COM object that has been separated from its underlying RCW cannot be used.
Seeing your suggestion to create a log, I was going to send one along to help out the trouble-shooting process. But here’s the deal. When I change my settings to enable logging, the problem went away. Everything worked perfectly. Then I turned off logging, and the error returned. I turned logging back on, and the problem went away.
Great, I thought, but that wasn’t the end of the story. After a couple times toggling back and forth, I received a different error with logging turned on:
Unable to load bitmap.
Hope this helps in some way.
BTW, is there a way to retain the folder I choose when I batch export? It always makes my find my working folder over again, which is about 10 folders deep. Starting in the location of the current Excel file would help.