Code:
UPDATE CAMSSTG.NDW_BOP_DETAIL_M_TEST
SET FISCAL_MONTH = V_FISCAL_MONTH
WHERE MODIFICATION_DATE BETWEEN '1-DEC-2002' AND '31-DEC-2002';

UPDATE CAMSSTG.NDW_BOP_DETAIL_M_TEST
SET FISCAL_MONTH = V_FISCAL_MONTH
WHERE MODIFICATION_DATE BETWEEN TO_DATE('1-DEC-2002', 'DD-MM-YYYY')
                            AND TO_DATE('31-DEC-2002', 'DD-MM-YYYY');
now you tell me what's so difficult?