Firmware update fail (7.9.1)

Hello Everyone.
I can't update my BMPCC 4k firmware to 7.9.1. I keep getting an error "Update filed, please check connections"
I have tried different cables, different USBs type 2 and 3, different computers (both Macs), and on mains and battery and combinations of. Nothing has worked so far.
The update will fail, and my PCC is bricked until I pull the batteries and/or mains for a few minutes.
I am trying to go from 6.1 to 7.9.1 - could this be causing the problem?

Hi All.
I worked out what this didn't work. It was too much of a. jump to go from 6.1 to 7.9.1
I upgraded to something like 6.9 first, then up to 7.9.1 which has worked fine.

Hi All.
I worked out what this didn't work...

Good you found a way, Simon.