Hi Ian,
I've also not managed to get the upgrade via USB to work - in the same way, from the previous software version. The last step doesn't work for me.
Worse than that - it appears to have trashed my USB stick (which had other things on it!) to the point of reformatting :-(
By any chance, did you have the port you were using configured as something else, such as 'transponder out' ?
If so, it will simply use it as a raw device and blat data to it.
We saw a similar issue of the the port configured as Flarm-IN, which gave very strange results when reading raw data from the USB stick
When using USB/RS232 bridge configuration, there is no way of knowing what the end device is, in the same way you can know for a GPS, or an RTL-SDR.
Sorry to hear it trashed the USB, I hope you have a backup
Thx
Lee