Oracle Forms

Hi all,
I have a field (not a database item of the block ) of LOV object and a button next to it to trigger to the LOV list item.

However, whenever, i click on the button, FRM-41042: No such property for SET_ITEM_PROPERTY will be prompted. Though the list item do appear and the item can be set into the field.

Here is the procedure called by the when-button-pressed trigger of the button.

PROCEDURE press_lov_btn IS
v_lov_name varchar2(30);
v_sel boolean;
l_target_item varchar2(100);
BEGIN
l_target_item := NAME_IN ( 'SYSTEM.TRIGGER_BLOCK' ) || '.' ||
GET_ITEM_PROPERTY ( NAME_IN ( 'SYSTEM.TRIGGER_ITEM' ), PREVIOUSITEM );
IF l_target_item != NAME_IN ( 'SYSTEM.CURSOR_ITEM' ) THEN
GO_ITEM ( l_target_item );
v_lov_name := get_item_property ( l_target_item, lov_name );
END IF;
v_sel := show_lov ( v_lov_name );

if not v_sel then
raise form_trigger_failure;
end if;
END press_lov_btn;

Any one know the error is due to the setting in the field or that in the button?????

Thanks a lot.