The manual upgrade to 17 worked!
It then rebooted and now I'm on 17-0.
Thanks a lot for all of your time
You are geniuses! :applause
Next, I also already updated the roll-up patch (patch 11) on 17-0.
That was also successful.
Then I tried to upgrade to the latest version (18.2) via the automatic updates as listed.
That also succeeded :)
Thanks again!