I ran the Homegroup troubleshooter on all three computers.
In each case it reported that a problem was found that could not be fixed automatically.
It did not say what the problem was.
It advised me to remove then recreate the Homegroup, which I did.
This did not resolve the problem of some computers being unable to access shared libraries on other computers.
Given that I have discovered no utility in either Libraries or Homegroups, I would prefer to dispense with them entirely.
All computers are members of the same Workgroup.
The current status is that all computers can access shared folders on CPU4 and CPU8; however, neither CPU4 nor CPU8 can access any shared folder on CPU7.
In each case, I receive the following message:
"Windows cannot access
\\CPU7. You do not have permission to access
\\CPU7. Contact your network administrator to request access."
Can you explain what is going on?