By default, an L-series device that is connected to a host but not logged in will disconnect after a certain period of time. This is to prevent too many idle sessions from sitting at the Windows login screen for extended periods of time, using up available sessions.
However, in certain configurations (such as when a terminal has been configured to ‘auto-connect’ to a host) this can be detrimental. To disable this function, add a REG_DWORD entry of LogonTimeout in HKLM\System\CurrentControlSet\Control\Terminal Server\WinStations\NC-Vspace
Set a value of the desired time (in seconds).