sql select sum stored procedure

Oracle 8.1.7

This SQL works fine in SQLPlus but does not work in a stored procedure.
In a stored procedure it does not like the (SELECT SUM( .

select rh.case_no into v_ct

   FROM w_wage_employer rwe, w_rg101 rh, w_wage_case rwc

   WHERE rwe.cd_disposition         = 'NONE'              AND
         rh.cd_case_category       IN ('06','08','09')    AND
         rh.case_status             = '2'                 AND
         rwc.id_rg101               = rh.id_rg101         AND
         rwc.id_wage                = rwe.id_wage         AND
         rwe.amt_wages - ( SELECT SUM(gwsc.amt_payment)
                    FROM w_gws_client gwsc
                    WHERE gwsc.cd_source            = rwe.cd_source   
          AND
                          gwsc.case_no              = rwe.case_no     
          AND
                          gwsc.dt_run               = rwe.dt_run      
          AND
                          gwsc.log_no               = rwe.log_no      
          AND
                          gwsc.cd_income            = '1'             
          AND
			  gwsc.is_income            = 'I'                        AND
                          gwsc.dt_claim             >= rwc.dt_month_1 
          AND
                          gwsc.dt_claim             <= rwc.dt_month_3 
          AND
                          gwsc.client_no             = rwe.client_no)