Oracle Forms

i want to populate a list item based on value entered in a text field.
the text field is fth_code and if the value of fth_code is 'PMT' populate list fth_party_code with "SUPL"
and if it is "RCT" then populate fth_party_code "CUST".

i wrote this in the WVI OF FTH_CODE.
but when i run form and enter value in fth_code,i get error,

frm-41331 Could not delete element from fth_party_code.

DECLARE
SUPL varchar2(200) := 'SELECT SUPL_NAME,SUPL_CODE FROM SUPPLIER_MASTER'; 
CUST varchar2(200) := 'SELECT CUST_NAME,CUST_CODE FROM CUSTOMER_MASTER'; 

v_rg_id recordgroup;
v_err NUMBER:= 0;

BEGIN
IF  :FTH_CODE = 'PMT' THEN
		v_rg_id := create_group_from_query('recgrp1',SUPL);
ELSIF :FTH_CODE = 'RCT' THEN
		v_rg_id := create_group_from_query('recgrp1',CUST);
END IF;

v_err:= populate_group(v_rg_id);

clear_list('FTH_PARTY_CODE');
populate_list('FTH_PARTY_CODE',v_rg_id);
DELETE_GROUP(v_rg_id);
END;

please anyone can suggest what is the problem actually? thanks