You cannot use a smart card certificate to log on to a domain from a Windows Vista-based or a Windows Server 2008-based client computer
In a Windows 2008-based domain that is using the Active Directory directory service, you enable a client computer to use smart card authentication to log on to the domain. However, when you try to log on to the domain from a Windows Vista-based or a Windows Server 2008-based client computer, the logon process may fail, and you may receive the following error message:
No valid certificates found
Check that the card is inserted
This issue occurs if the smart card certificate does not contain Microsoft Extended Key Usage (EKU).
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB955558.