Registering Production Pack Plus

I bought a Roland A800 Pro midi keyboard controller, and let the kids plug it in and get started with Garageband.  Now, a year later, I've finally decided to start playing with the Cakewalk software that came with it (sonar, rapture etc).  But I can't find the serial number for the software to complete the registration.  What am I looking for? There are 4 digit numbers on the CD and a longer number on the small installation guide, but the registration process doesn't recognise these as valid serial numbers.  Should there have been a sticker somewhere in the box?  What should the serial number start with?  Any help gratefully received.

Thanks

Donald