The install just completed successfully!
After reporting the problem a week or so ago, I have installed various Win 10, etc. upgrades and rebooted several times.
Still no success installing this morning. I received the same error.
So I paused KIS virus protection and ran Program Install and Uninstall Troubleshooter:
http://aka.ms/Program_Install_and_UninstallIt did not list CS, so I ran it with 'program is not listed'. The Troubleshooter found an fixed errors.
Then I closed Firefox, and ran the CS upgrade again. It completed the install very quickly.
BTW, I run Malwarebytes Anti-Malware also, and did not close or pause it before the installation.
All is well again.