When a map is scheduled the resultant windows scheduled task runs under the account entered in the username and password fields on the Schedule map window. This windowsad account must have access to the GP SQL databases as part of the DYNGRP and be setup with the correct permissions in the SmartConnect security window.
This account can also be viewed by right clicking on the Scheduled task in Strart à Control Panel à Scheduled tasks and selecting properties.
By default the scheduled task is created on the local computer that the GP client is running on but can be created on one central server by specifying server in the setup. If these options are blank the scheduled task is created locally for workstations.