@xander2m Thank you
Yes I did as exactly as you suggested...with bootloader unlocked and debugging enabled. Everything seems to start
then I get this message:
Unable to Mount Nexus 7 (2013) WiFi
Unable to open MPT device "[usb:002,010]"
Both Nexus 7's gave the same message.
The installation ends with that message on Linux Mint
and the brown Ubuntu screen on the Nexus 7.
The Ubuntu screen says...
Ubuntu Touch (CWM-based) Recovery v6.0.4.6
and gives me options...all of which I have tried.
The very last line of the Ubuntu terminal reads...
E: Can't open /cashe/recovery/last_install

Have also tried to install ubuntu-device-flash after getting the repository from repo.ubports.com and then
apt install ubuntu.device.flash
But it always ends with...
E: unable to locate package ubuntu.device.flash

I can try to show you screen shot photos if there is a way to post them here.
Thanks for your help