Gonzo, are both your BIOS damaged then? Are you able to recover via USB flash? Could try flashing 1401 in the good chip, that might still work if you're lucky. Then do a direct copy to the faulty chip from the BIOS itself.
I did try flashing 1502 again, this time I was successful. I've noticed a BIOS update always needs to be flashed at least twice and left powered for awhile in order to get it to "set". The error message did catch me by surprise though, thought it was a joke message or virus thingy. Then I remembered Intel MEI has a slim chance of getting wiped from the BIOS because of a bad flash, so that sort of answered it for me
I think 1502 should be fine once you get it up and running soon. But I'm downgrading back to 1401, system gets problematic when I tired to use it.