Well, I’ve done as you suggested.  Thank you.  I have even tried going back to scratch, removing python and reinstalling and after a very large effort in de-tangling the various libraries, things are up and running again, this time with CUDA11.1
I can’t thank you enough for pointing me in the right direction.  Things are starting to run, so i’m on to the next phase of wrestling with memory and when and where to pull things over to the cpu.  But things are looking up.  I’m sure there is a very good reason for all the juggling of data from one device to another but, as a beginner, it’s difficult to be forced into that level of control.  I’m sure one day it will all just make sense.
Thanks again.