I downloaded the free version 4.0. It installed and overwrote pro version 3.2.10. The free version 4.0 worked. I then deleted the free version and executed the downloaded file ninja-setup-pro-4.0.exe. Pro 4.0 installed and worked.
Thank you for replying to my inquiry. It appears that I resolved the problem by completely uninstalling the previous 3.2.10 Pro and installing Pro 4.0.