Installing SSL User certificate

I’m trying to test the use of x509 user certificates for authenticating users automatically with a web server.

I’ve tried a couple of different vendors (Verisign and Trustcentre) and it appears that both certs have installed. Certainly, in IE I can open the certificates box and see both of them installed.

However, when I then go to my server I am prompted with a “Choose a Digital Certificate” dialog, but there are no certificates listed.

Any ideas?