Then, the serial number you put in to get the upgrade price is the one on file at NI "your registrations and serial numbers" area. Your old serial number.
When I downloaded the upgrade I also received the old KP2 Installer with the new GPO 4 - which I lamely tried to install again and again, thinking it was the installer for GPO 4. Just look in the GPO 4 folder - the correct installer is there. Throw the other one out!
After I installed GPO w ARIA, I tried to drag and drop the activation card onto the opened ARIA app with no success, either as a Standalone or as a plug in within DP.
What I finally did was download the actual file, and take that physically out of my downloads and drop it onto the ARIA player, after which my player was successfully activated.
I know this may be old news because I took so long to upgrade but there you go.