Hi Rich,
I've done an option upgrade 14 days ago on my 8753D (with the CPU 000 board, which is probably also in your VNA). I've got the same error, because I did not flip the jumper (there is no A9 dip swich on the CPU 000 board, but is the S400 instead). After I've correctly flipped the S400 #8 switch, the option upgrade went flawlessly.
Greetings,
Leon
