After a Time Machine file restore in macOS you may encounter this activation error, even if the license is properly activated in the iLok License Manager software.
How to fix this:
You MUST first be logged in as a user with administrator access, (if you only have one user / login on your Mac, then your account will have administrator access).
Open a macOS terminal:
then copy this command into the command line and press Return:
You will now be prompted to enter your macOS current user session.
This should activate your product license properly and fix the problem.