The last snippet of my log read:
So I went into regedit and found no Key by that name in HKEY_CLASSES_ROOT\CLSID.
I created one, just an empty key, and re-ran the installer. It failed again, this time throwing an error:
Ok, so I created that key too, and re-ran the installer, it failed again, this time reporting:
Oy, it clearly doesn't like the fact that 'something' is missing with Explorer shell handler. Fine, I re-created that key too. Yet another missing key:
Eventually I tracked down all of the missing keys...
But that did not help. The log doesn't show any errors but it still fails with a 1603.
Diag details:
Ok, so this isn't working. I tried to use the installer... it likewise fails. So I tried using Windows to remove the program. It complains I have to use the Wizard.
So I ran the Microsoft tool. https://support.microsoft.com/en-us/help/17588/fix-problems-that-block-programs-from-being-installed-or-removed
It apparently found something, fixed it and then removed the .12 version of paint.net.
I could then run the .16 installer successfully.