KB4014984 doesn't install on Vista (standalone either)

Hi Great White North, (COMPLETE SOLUTION TO PROBLEM)

Happy Easter.

I tried the method you suggested posted by Greenhillmaniac by downloading his Microsoftrootcertificate2011.cer file and installed it by the command line method he suggested.  Like Mikey said, this method "worked like a charm", and windows update installed the April 2017 rollup perfectly.  The "meticulous scientist" in me (you can probably tell by the way I post) was curious as to why this method worked so much better than the solution I posted yesterday, so I ended up restoring the Windows Vista partition several times and running several trials to answer this question.   It turns out that his certificate file is identical to the one I exported from a Windows 7 computer; however, the "command line" method of installing this certificate is a superior method of installing it that the method I was using, which was to import the certificate into the Trusted Root Certification Authorities tab by using the import button.

To anyone else who may encounter this problem, my recommended solution is outlined below:

Obtain a copy of the Microsoft Root Certificate Authority 2011 certificate either by downloading it (see previous posts in this thread) or exporting it from a more modern up to date computer (I used a Windows 7 computer.)  I would recommend also obtaining the Microsoft Root Certificate Authority 2010 certificate, but for the purposes of this solution the 2011 certificate alone works fine.  Copy this root certificate file (or files) to your C: drive by clicking the My Computer button, then the C: hard drive icon, and move or copy the file(s) to this window (for simplicity, do not put the file inside any folder on the C drive.)  Click the start button, then move the cursor to programs, then the accessories folder, then RIGHT CLICK the command prompt icon and choose "Run as administrator" from the pop up menu that appears.  Type cd\ and hit enter.  Then type certutil -addstore "Root" "c:\XX.cer" and hit enter. Type this command exactly as written including the quotation marks except substitute the name you chose for the certificate file for the XX.  You should get a confirmation message telling you that the command action was successful.  Run this command twice if you are installing both the 2010 and 2011 certificates.   Close the command prompt window and restart the computer.  You should now be able to install the Security and Quality Rollup April 2017 now either by running Windows update (easiest way) or by using the stand alone installers that I discussed yesterday (earlier in this thread.)  You can now delete the Microsoft Root certificates from your C: drive, or move them to a storage folder, or just leave them where they are (they won't hurt anything.)  My thanks to GREAT WHITE NORTH and GREENHILLMANIAC for their contributions to this solution.