Clarification: It is not necessary to uninstall Dorico if the “severe installation error 1603” occurs. Just install and run the Steinberg Download Assistant, click on “Dorico 1” and select the Dorico 1.1.0 installer (ca. 250 MB). The Halion engine/samples do not need to be reinstalled.
Don’t forget to reboot after installing.
Side question: Can we get an updated version of the popover reference PDF? Thanks!