The Windows Installer Service Could Not Be Accessed

The Windows Installer Service Could Not Be Accessed
Help sites say to unregister and reregister the msiexec.exe file and if that doesn't work to reinstall the .exe file. Before doing these, type "services.msc" in the "run" box of the "Start menu". Toggle down to the "Windows Installer" service. Make sure it's in the "started" (not "stopped") configuation. In my case this was sufficient to eliminate the error message.

I'd assumed that having the service "checked" in "msconfig" was sufficient to activate the service.

Microsoft error site

Installer exe file and path (XP) "c:\Windows\System32\Msiexec.exe"

How to manually register a file - sadly neither unregistering nor registering will be confirmed