When you enroll a certificate on a computer that is running Windows Vista or that is running Windows Server 2008, you are prompted to insert a smart card even though a smart card is already inserted. After you unplug your smart card and then plug it in again, the certificate enrollment process continues successfully.
However, if the smart card and the reader are integrated into one unit, you cannot unplug the smart card. For example, if you use a USB token device as a smart card, the certificate enrollment process does not continue even after you unplug and then plug in the USB token device. Therefore, the certificate enrollment fails.