It rejected my Bryce 4 serial number during the installation process. Told me it was invalid. I called the Customer Service number on the back of the card (I think that's where it was.) Saturday afternoon. They asked if I had registered Bryce 4 with either them or Metacreations. I had. Then they asked for my name and a couple other questions and found me in their database. Then they asked for my Bryce 5 serial number, and registered it. Then they gave me a new serial number. I had to enter this number in place of the Bryce 5 serial number. This number also made it bypass the request for the Bryce 4 serial number. And I was up and running.