Thank you, now is clear.
Just a minor modification in the TRANSFORM query, should be like:
TRANSFORM Min(Switch([CrosstabHeading]="BeginDate",[STARTING_DATE],[CrosstabHeading]="EndDate",[ENDING_DATE],1,[Owner])) AS Expr2
SELECT qselSubSystems.Subsystem
FROM qselSubSystems, tblCrosstabHeading...