I had a similar problem with Windows Update... it would not update.
I found a simple solution, delete the SoftwareDistribution sub-directory within your windows directory. The caveat is you'll lose your update history... oh well??

When you retry Windows Update the system will re-create the missing directory and execute the update flawlessly.

I've never got MS fix-it to recommend anything useful. But, I've only been repairing PCs for 25 years and have not encountered everything yet.