It was time for the software to get updated and I was asked to complete registration/activation. On entering serial number it said this has been registered already and asks me to enter the serial number again and again. I bought the product new rom a shop online.
The programme works well on my computer otherwise.
Hopefully you bought a genuine new boxed set of MMM .
If it has been pre-owned then you should have got all the discs, manual and box. You will have to get the previous owner to ask Magix to de-register the software.
If you have the disc only then you may have a non original disc.
Contact Magix sales and ask them if your copy is legal and registered to yourself.