Try going to C:\Program Files\Steinberg\Cubase , and run Cubase as administrator. Any difference?
If that doesn’t work, try this fix that someone posted a while ago. I don’t know if it still works in modern versions of Windows, but it’s worth a try:
1.Open the Control Panel
3.Select [Advanced Settings]
4.Under [Performance] select [Settings]
5.If DEP is available on your system, a DEP tab will be present in the Performance Setting dialog. Select this tab if it’s present (if it’s not present, then your system doesn’t have DEP).
6. Select [Turn on DEP for all programs and services except those I select]:
7. Add SYNSOPOS.EXE from the folder [C:\Program Files (x86)\eLicenser\POS] or wherever you have this file.
If neither of these work, I would recommend contacting support directly through your MySteinberg. Click the “Register eLicenser / software & Enter Download Access Code” button first.