When trying to use a client certificate generated by an AspEncrypt-based certification authority (CA) to access an SSL-enabled site with the option "Require client certificates" set, the client certificate does not show up in the "Client Authentication" dialog box presented by the browser.
You must include the root certificate (the one used to sign your client certificate) in the list of trusted root certificates on the web server. Furthermore, the root certificate must be placed in the "local machine" portion of the Root certificate store.The following Microsoft KB article describes how this must be done: