Hi,
I just wanted to post this in case anyone has had a similar problem activating Mixpack2 in Logic Pro X on Mac OS X. Hopefully anyone Googling will find this topic and will be spared some heartache/head scratching.
I kept trying to authorise my plugins with my legitimately obtained key and it kept just saying "The authorization data is invalid".
What i eventually realised was, it's not enough just to copy and paste your name and key into the edit boxes then click "Authorize". You have to press the enter (return) key after typing/pasting your name, and then press it _again_ after typing/pasting your key. The authorisation button should now work (can't remember if you click or press enter again).
Hope I helped.