Welcome to the Autodesk Forums!

Hi,

Most likely you need to try at first to reset AutoCAD license:

you need to follow this article:
http://knowledge.autodesk.com/support/autocad-for-mac/troubleshooting/caas/sfdcarticles/sfdcarticles...
or "illustrated" guide here:
http://upandready.typepad.com/up_and_ready/2013/02/reset-standalone-licensing-on-the-mac.html

Then you need to activate AutoCAD again with your serial.

Maxim