I have changed the table name so now have
WHERE (((best_2011.start1) Between DateSerial(Year(Date())-1,Month(Date()),1) And (DateAdd("m",1,(DateSerial(Year(Date())-1,Month(Date()),1))-1))) AND ((best_2011.btec_first_unit1)="yes")) OR (((best_2011.btec_first_unit2)="yes"));
This is wrong...