Record Group functions - Problerms with a function Get_Group_Selection

Question

Anywone knows how to delete a record from a record group, i have this code below on the trigger KEY-DELREC, every time i delete a record this code is execute. The problem here is that i whant to delete a row in a record group but , i can't use the function Get_Group_Selection, to find the number of the row i want to delete, when i use the function Get_Group_Selection, it gives me the error FRM-41087 .
Can aywone help me with that , it's urgent!!
Thanks
DECLARE
ora_err NUMBER;
rg_id RECORDGROUP;
the_Rowcount NUMBER;
gc_id1 GroupColumn;
gc_id2 GroupColumn;
v_art_grp_no number(3);
v_descr VARCHAR2(20);
v_art_grp_no2 number(3);
v_descr2 VARCHAR2(20);
v_ctn NUMBER := 0;
v_row NUMBER;
begin
rg_id := Find_Group('REG_REPAIRS_COMPONENTS');
the_Rowcount := Get_Group_Row_Count( rg_id );
--** Make sure the column name specified exists in the ** record Group. */
gc_id1 := Find_Column('REG_REPAIRS_COMPONENTS.ART_GRP_NO');
gc_id2 := Find_Column('REG_REPAIRS_COMPONENTS.DESCR');
FOR j IN 1..the_Rowcount LOOP
     v_ctn := Get_Group_Selection(rg_id,j);
     v_art_grp_no := Get_Group_Number_Cell(gc_id1,v_ctn);
v_descr := GET_GROUP_CHAR_CELL(gc_id2,     v_ctn );
if UPPER(v_descr) = UPPER(:system.cursor_value) and UPPER(v_art_grp_no) = UPPER(:repairs_components.art_grp_no) then
     Delete_Group_Row('REG_REPAIRS_COMPONENT',      v_ctn);
     delete_record;
     end if;
     END LOOP;
end;

Answer 1

Thanks for the HELP!
But now i have an other problem that is when i invoke the when-validate item trigger it searchs the field for a value that´s is equal to value in a record group and if it finds it, it raises
raise_form_trigger_failure and displays a messagem, it works fine but if a press the button save or back it displays the message and after if i press the default button to delete again it doesn´t work .