Windows notices inactivity of a logon session, and if the amount of inactive time exceeds the inactivity limit, then the screen saver will run, locking the session. Fix: (1) GPO: Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options!Interactive logon: Machine inactivity limit (2) REG: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\System!InactivityTimeoutSecs