To activate your product, you will need to use your 2012 serial number instead of your 2011 serial number. You can find this information on your Subscription site. Your product key is not unique and will be the same for all Max 2012 products. It should likley be the same as your 2011 except with a D instead of a C, unless your product suite has changed. However, unless you use your 2012 serial number you will not be able to activate.
Your information is on the Subscription site. If you cannot find it, you may want to contact Autodesk Subscription services or your reseller.
Start with some of our most frequented solutions or visit the Installation and Licensing Forum to get help installing your software.