Cubase 9.5.40 update - How to Solve the 1603 Error (PC)
Mine was missing the file indicated in the error pop up.
So, if you just goto C:\ProgramData\Steinberg\Audio Export Post Process Scripts and see if OpenInCubase95_64.aepp is missing
If it is, just recreated a blank file and name it “OpenInCubase95_64.aepp” and ensure .aepp and not .txt file type of course.
That allowed to update to continue.