You can try ..
CurrentDb.Execute "INSERT INTO tblPySub([Date],[driverID])
VALUES(#" & format(DateAdd("d", i + 1, Me.StartDate), "yyyy-mm-dd") & "#," & Me.DriverID & ")"
but there might be an issue with me.startdate, so before the 'For i= ... ' command add a temporary line..
msgbox me.startdate
and make sure you see what you are expecting.