I wanted to add further detail:

Cable driver 6.85.10.0 works. That's what I am currently using.

But 6.86.11.0 does NOT work. Something has broken between the two versions, at
least where the N800 is concerned.

I discovered this when I updated PC Suit to the latest build of 6.86.
Immediately I was back to the same problem of being unable to flash my tablets.
This needs to be investigated.