Citazione:
Wordfence could not get an API key from the Wordfence scanning servers when it activated. You can try to fix this by going to the Wordfence "options" page and hitting "Save Changes". This will cause Wordfence to retry fetching an API key for you. If you keep seeing this error it usually means your WordPress server can't connect to our scanning servers. You can try asking your WordPress host to allow your WordPress server to connect to noc1.wordfence.com.
Ho già provato a fare quanto indicato (Opzioni - Save Changes) ma non funziona.