The client system is unable to download the PAC File from the PAC File Management System and connect to the Web Security Service.
Network environment or firewall is blocking access to the IP addresses where the PAC File is hosted on PAC File Management System.
If your firewall does not allow white-listing "pfms.wss.symantec.com" by DNS, allow the following static IP address: 18.104.22.168 (November 7, 2020).
If you employed the PFMS before November 7, 2020, the following IP addresses were used. Firewall rules for these IP addresses can remain in place in the near-term as a precaution for failover or fallback. A follow up announcement will be made after the existing IP's have been fully decommissioned: