By default only the current logged in user or an administrator is able to unlock a workstation that has been locked. Workstations can be locked by selecting "Lock Now" from the Ctrl-Alt-Del menu or by password protected screensavers. When the current user unlocks the system their logon session is restored; when an administrator uses his credentials to unlock the system then the current user is logged off before another user can log on.
This can be a problem when computers in public areas are locked and put out of commission. Regular users are unable to unlock the computers and an administrator must be called. HIPAA and SOX requires all stations to be locked when not in use so many systems are set to automatically lock when not in use so this is becoming more and more of a problem on nursing stations.
A third party product called "Unlock Administrator" ( http://www.e-motional.com/ULAdmin.htm ) solves the problem allowing you to specify exactly which users are able to unlock systems. In situations where many users are sharing the same generic logon session, the program allows selected users to unlock the computer without logging the current user off. Logs are kept to know who unlocked the system and when. Runs under Windows 2000,XP,2003 but not Vista.