Found a solution. I noticed that there had been a number of automatic Microsoft security updates that have failed over the past few months that had gone unnoticed, when I attempted to install one of those updates manually I got the exact same error.
Here's the link that provided the workaround:
https://answers.microsoft.com/en-us/windows/forum/windows_8-performance/get-error-1723-there-is-a-problem-with-windows/3d68fc4b-c968-4796-a270-27027a52de3f
Marilyn O (Microsoft) listed under "All replies" provided the solution, to run "sfc /scannow" as administrator under cmd.exe
