Hi Wim!
Thanks for your answer!
It worked now - The step 2 refers to this download?
(The link in the support-page is broken, but I found an old forum post, referring to the [same page] )
Step 2, Program install
(Rhino 6 update/install error rhino.msi: -2147023293 [SOLVED])
https://support.microsoft.com/en-us/help/17588/windows-fix-problems-that-block-programs-being-installed-or-removed
When I used the tool to fix Rhino Installer Engine, it worked perfectly.
Anyways, thank you!