We have a Dell laptop with Vista Enterprise installed, per Army requirements. We can log in locally, connect to and manage the machine remotely across the network using an administrator account on a smart card. The computer is joined to the army domain. When we try to log in to the machine using the card reader, we receive an error - System could not log you on. An untrusted certificate authority was detected while processing the domain controller used for authentication. This has occurred on more than one machine, but the problem goes away if we go back to XP. Also, when I logged in locally to the machine yesterday, it requested a smart card to activate the Windows, and it accepted it using the card reader with no problem. Have updated the drivers, as well as installed an external card reader. Same results. Dell suggested updating the BIOS, but that had no effect either.

Did you ever find out exactly what the issue was. I have been working on the same issue for one week now. Any insight would be appreciated.

Not sure if you guys/gals are still looking for an answer but I ran into this same problem today and found a fix. You need to check the certification store in the certification snap-in via mmc.exe. Navigate to the Trusted Root CA folder and make sure you have the JITC cert and US IPSec CAC Login Cert(issued by NETCOM) installed. If not, you can export them to a disc from a system doesn't have that issue and import to the snap in. Performed on 3 systems and after a reboot I was able to log-in with no problem. Hope this helps.