Configuring Your Verisign Certificates to Avoid Warnings
If you've heard of customers reporting "website certified by an unknown authority" messages, read on.
This message results when secure servers with step-up certificates, such as VeriSign's Secure Site Pro, fail to send an intermediate CA certificate along with the signed certificate. It's easy to overlook the step during certificate installation but, for your server to properly initiate 128-bit sessions with browsers, you must install both the intermediate CA certificate and signed certificate.
Installing VeriSign's intermediate CA certificate only takes a few minutes. Some resources: