Q: Bought a new iMac, how do I transfer license?

Is your Aperture version a full Aperture 3 version or an Upgrade from Aperture 2?

If it is an upgrade, you need to enter the Aperture 2 (or 1) serial number as well.

If i is the full Aperture 3 version, check, if you entered the serial number correctly - some letters can easily be confused, 1, l and I, or O and 0.

And don't enter the numbers from the numeric part of the keyboard.

See this support article:

Troubleshooting Professional Application Serial Numbers

If you cannot find your Aperture 2 serial number, or cannot make Aperture accept your Aperture 3 serial, contact Apple, see Pro Application Replacement Serial Numbers

Regards

Léonie