This occurs when the "Requested by" field on the query and output schedule record being run is null. Normally this field cannot be null, as TA will not let you leave this field blank. However, if the user that was selected in the 'Requested by" field was removed from the Brief_Names table by a change brief name, then all records using that Brief_Name will have it set to null instead. So any scheduled Query and Output runs using that user will lose their "Requested by" and become null and fail.
To resolve the issue, just select another user for the "Requested by" and rerun the Query and Output.