VeriSign Intermediate Root CA Expired
The VeriSign Global Server Intermediate Root CA for IIS expires on January 7, 2004, this has cause some interruption of few major web server, if you using Verisign cert with client certicate, you will get the following error.
403.16 - Client certificate is untrusted or invalid.
The client certificate has expired or is not yet valid.
More detail refer
http://support.microsoft.com/?id=834438