@Paul-Miller Can you tell us where you bought the software? If you got it from a third party seller it is possible that the seller hasn't informed Magix of your purchase yet. In this case you need to contact your seller. Also please check your serial number for typos.

https://www.magix.info/us/support/article/troubleshooting-error-code-14--12/

You can also try the following tricks. Start Music Maker as administrator (right click on the program icon), temporarily disable your firewall or Windows Defender. Maybe it will work after you rebooted your Windows computer.