There seems to be a bug / issue where ASP.NET cannot access the Private key in a certificate. You can replicate the steps to recreate the issue at the below url. If I'm missing something please let me know. Everything is working fine in production on II6 Server 2003 however going to a brand new Server 2008 R2 and IIS 7.5 one cannot give access to a cert in the "Local Computer\Personal" cert store even if you grant "Everyone" full access.
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