I have purchased MAGIX Photo Manager Deluxe 17 but can’t authenticate the product, it advises that the code has already been used on another email address.
From what you write I assume this may be from a previous owner? If so, that owner must advise Magix that he/she has sold the product to you and that, therefore, the serial key must be disconnected from his/her Magix Account. Unless this is done, and until Magix resets the account data for the previous owner, you will never be able to register and activate the product in your own name or to your own account.