The Issue:
We requested a new certificate for our website from a CA. We applied the certificate on the Internal IIS6 web server. I then exported the certificate including keys and imported onto our ISA 2006 firewall.
I then went into the publishing rule for our website and updated it with the new certificate.
When external users went to our website using https they got the following error:
Error Code: 500 Internal Server Error. The target principal name is incorrect. (-2146893022)