Oracle Forms

Hello!

i have a list_item with name NOMBRE and in a NEW_FORM_INSTANCE trigger i have the following pl/sql block to populate it:

declare
grp_producto recordgroup := find_group('RECORD_PRODUCTO');
lst_item item := find_item('PRODUCTO.NOMBRE');
status number;
begin
status := populate_group(grp_producto);
clear_list(lst_item);
populate_list(lst_item,grp_producto);
end;

when i run the form, this message appear
FRM-30351: No list elements defined for list item.
List NOMBRE
and the list appear without elements
...can somebody explain me the solution or if i have to do another thing to populate the list?

Thanks