How did you migrate Aperture? Did you reinstall it or simply migrated it using Migration assistant? Pro Apps are best reinstalled using the installation media. You can reinstall directly the Aperture 3 upgrade and then update to the current version using Software update.
See this: http://support.apple.com/kb/TS2005
Check, if all letters are typed correctly. Don't use the numerical keypad to enter the numbers and check if caps lock is accidentally enabled.
Enter all serial numbers for all previous versions, beginning from Aperture 1, if your Aperture 2 is an upgrade.
If you cannot get Aperture to accept your serial number, contact Apple: Pro Application Replacement Serial Numbers
Regards
Léonie
Sorry, Frank,
your post did not show 😟