Please check if the source IP in the DNS configuration of WebGuard is correct, whether there remains IPS is wrong or no longer in use. Please check if the firewall of source website blocked the IPs of WebGuard nodes. see the FAQ for details. If the firewall of ISP blocked ,the IPs of WebGuard nodes. please contact the ISP to unlock and add the IP segments to whitelist. If you have not any firewall on server, please contact with your IDC, and add the IP segments of WebGuard to the whitelist of the IDC.