I have developed a (unsigned) smart card minidriver for Windows logon. It works for Vista, Windows Server 2008 R2, win7 when the PC is in the domain. When the PC is offline, the smart card logon works for Vista, but not for Windows 7 and Windows Server 2008 R2. The error message displayed on the logon screen is "The system could not log you on. The domain specified is not available. Please try again later."
Credential caching does not appear to be the problem. i can log on with password when the PC is offline.