I had the same problem,
you can fix it in a simple way
Open internet explorer
Go to tools( alt+x) at the top right corner & select internet options
Under Internet options, go to the last tab (advanced) on the right
Under advanced settings, scroll for security settings &
check allow software to run even if the signature is invalid
then when you open your apple updates, check the updates you want to download
& from the tools option above, select download only
Once downloaded, run the setup file as admin
This is a pain, but it worked for me 🙂
Also unchecking the check for signatures for downloaded programmes in the advanced security settings helps sometimes
Hope it solves your problem