Have you enabled MAC Authentication on your AAA Profile and specified the MAC Authentication Server Group? Go to your node where you will be making the change. Then go to Configuration -> Authentication -> AAA Profiles -> AAA -> then select your AAA Profile.
Once your AAA profile is selected, you will see a list of Authentication settings 802.1X Authentication, 802.1X authentication Server Group, MAC Authentication, MAC Authenticaiton Server Group, ...
Click on the MAC Authentication and create and configure the profile. The key thing here is to remember that the MC is sending the MAC to the Authentication server and doing a database lookup of the MAC as if it were a user, so the delimiter and case needs to be properly specified.
After the MAC Authentication profile is created, go to the MAC Authentication Server Group and select the server group that you will be authenticating against. If you have not created one, you will need to create/define a server first, and then create/define the server group.
I hope this helps,