read client certificate from httprequest C#

Question

I am trying to read an X509 certificate using Request.ClientCertificate but nothing is returned. The certificate is definitely being attached to the request because I can get the certificate information from the page sending the request.

I have tried reading the certificate from several different places but cannot seem to get it to work.

I started with code from this KB Article. In the requested page I tried to print out some information about the certificate but nothing was returned in the response.

This is running on IIS 5.1 and the communication is over SSL. This must be done using version 2 of the .Net framework

Why does the certificate seem to dissappear?