The algorithm for the Encrypting File System (EFS) smartcard certificate implementation in Windows Vista may cause data loss
The Encrypting File System (EFS) smartcard certificate implementation in Windows Vista ignores the Enhanced Key Usage extension if the extension does not specify EFS. In this situation, a certificate may be selected that is not intended for data encryption. Therefore, data may be lost if a Disaster Recovery Agent (DRA) is not configured or if the noncompliant certificate that was previously selected is not retained after it expires.
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB953152.