I am not sure if the problem you are seeing is the same as one addressed by these instructions, but it is probably worth trying:

You'll need your activation key after doing this (available from Norton Account).

In Terminal (/Applications/Utilities), enter the following command:

       sudo rm -f /private/var/db/com.symantec/Symantec.keychain

(you'll be asked to enter your admin password).

After doing that, restart, then reactivate the product.