This Microsoft article gives some ideas about why you are seeing that error message. Perhaps read it and consider trying out at least some of the suggested solutions, clearly at your own risk!
However, MEP MX is now a very old version (version 11, if I remember correctly) the current latest is version 20. Because of its age there is absolutely no guarantee that it will even install successfully under Windows 10, let alone run properly.
One other thought: you wrote Fixing problems .... after a Windows 10 Upgrade. Did you mean that literally, i.e., you have just upgraded your OS to Win 10, or did you mean a Win 10 Update?
I installed Windows 10 over the native Win 7 on an HP Miini. It’s performance was a tad slower than with Win 7, but kept up with software demands adequately. Until my Magix software did not. It seems that there is incompatibility with the Serial # and product code section of the Install, as that is where the error 1603 manifests. I am examining the install logs to see why. Any suggestions? I agree that MusicMaker is too old.(like its owner LOL. I appreciate your help,Terry
You have posted in the Movie Edit Pro forum, however are referring to Music Maker MX and your 2 previous posts also refer to Music Maker MX.
Can you clarify
which program you are having issues with.
. . . . installed Windows 10 over the native Win 7 on an HP Miini . . .
Which model of the HP Mini is this?
If the error is occurring during installation then it is very unlikely to run correctly if you manage to get it installed - Movie Edit Pro MX does not run on Windows 10