I installed Samplitude Pro X4 Suite and activated it successfully using the serial number that Magix provided. However, when I exited Samplitude and re-opened it, it asked for my serial number again, and then rejected it. So first it accepted my serial number, and then it rejected it.
Here's the error message: "The serial number you entered is invalid or may apply to another product. etc ... Error code -14."
That seems to indicate that I am using the wrong serial number. However, in my case, I have already activated and used Samplitude with the exact same serial number on the same computer. That is, the serial number is initially accepted, and I can use the software. It's only when I exit the program and try to re-start it that my serial number is rejected. I have uninstalled and reinstalled several times, but the problem persists.
I wonder if this problem might be a result of having previously installed a demo version of Samplitude Pro X4 on the same computer. Perhaps the CD version that I installed subsequently did not properly remove the demo version.