The issue occurs when you attempt to download the PAC file from ThreatPulse by entering the URL (https://portal.threatpulse.com/pac) on the browser address bar. The returned PAC file contains a line with the following error:
This issue usually occurs when connected through an explicit PAC file and the browser has automatic configuration script configured with the https://portal.threatpulse.com/pac URL. The browser is able to download the PAC file with this URL and effective as automatic configuration script.
To be able to download the PAC file by entering the https://portal.threatpulse.com/pac URL in the browser, you must remove the browser "Automatic configuration scripts" settings in settings.
Menu > Internet Options > Connections > LAN Settings > User automatic configuration file.
Menu > Tools > Options > Advanced > Network > Connections Settings > Automatic proxy configuration URL.