Adobe upgrades require a qualifying previous product. If the upgrade installer can't find a previous product on your computer, it asks you to enter the serial number of your previous product. This may happen if you are installing the upgrade on a new computer or new hard drive, for example.
Try the solutions in this document if you receive the error, “This serial number is not for a qualifying product. Please try another” when you enter a serial number in the Serial Number Upgrade screen.