I had the same thing happen and it asked me t do all updates and that some parts were missing. I tried several times, then Binged it and came here to find nothing. I always do a CCleaner Registry clean and then a normal clean after monthly updates. I also
save the old registry when asked by CCleaner. I decided to try restoring the registry first by going to documents and double clicking on the last saved registry dated to day, and that fixed defender.
I had CCleaner registry cleaner mess up another system a few months back by not allowing me to click on hot links in my MS Office 2010 Outlook which we use for mail here. Instead of opening the link it told me I did not have permission for that. I restored
the last registry clean and it fixed that one too. That was on a Dell 2720 All In One with an i7, 8GB of RAM, and a 32 GB SSD in front of a 2 TB rust drive.
Just navigate to where you saved them and look for the one with that day's date like today I looked there for this:
Double click on the one with today's date and then check. It fixed mine, a ASUS T200 with the 64 bit Windows 10 upgrade and anniversary update, it has 64GB of SSD, and 4GB of RAM running the Atom Z-3795 processor.
Hope that helps!
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