Definitely it is a problem of activation.
Could you try another method of resetting the license:
- restart your Mac,
- trash "FLEXnet Publisher" folder from /Library/Preferences folder ( the Library folder in the root of your Mac HD)
- now start AutoCAD again.
If you are on-line the activation should occur automatically an you should receive activation confirmation from Autodesk by e-mail.

Maxim