Thank you once again, Ivan, for your help. Unfortunately, we do not seem to be making much progress, and I'm getting more and more confused about why it is so difficult to accomplish what should be a relatively simple task.
And I do not understand your second para -- what 'first option'? what is an 'online account'? yes, I am trying to share the entire disk drive and yes, I do get the same permission error -- but why is that happening? what is causing it?
Nor do I understand your second para -- I only want to share Dell2 drives C, D, E and F, and PFG drives C, E and F and I've entered permissions for those drives only. So why has Users appeared and what is it?
I do seem to be able to access Network/PFG/Users/Public from DELL2 -- there are 7 folders there and they are all empty. But suddenly, I cannot access any drive in DELL2 from PFG -- when I click on Network/DELL2 from PFG, I get the same Network error as at the very top of this thread. I've checked again that I've fully shared all DELL2 drives. What on earth is happening?
If Users is where Microsoft puts its default folders, I deliberately do not use them at all. I prefer to put my files where I want them, not where Microsoft seems to think I should put them.
Are you (or anyone else) able to point me to somewhere where home networking on Windows 10 is explained in some detail?