This will happen on NGFW appliances running versions older than v14.2. We have changed Web Filter Category providers, so Category lookups will no longer work on NGFW 14.1 or older. In order to get your license (and Categories!) working, you'll need to upgrade to v14.2.
You should be able to start that process in Config > Upgrade, but let us know if you do not have the 'upgrade now' button on that page.Follow