INSERT BEFORE Trigger

Anytime I create an INSERT BEFORE trigger that includes a query on the
same table as the trigger is assigned, the insert does not happen
without error. I get 'INSERT 0 0'. It is like the query loses the insert
information, is this something that can't be done?

DECLARE
  checkit record;
BEGIN
  SELECT INTO checkit MAX(public.tblhudunits.sort_order) AS maximum,
MIN(public.tblhudunits.sort_order) AS minimum FROM public.tblhudunits
WHERE (public.tblhudunits.hud_building_id = NEW.hud_building_id);
  IF FOUND THEN
     IF (NEW.sort_order >= checkit.minimum AND NEW.sort_order <=
checkit.maximum) THEN
        RAISE EXCEPTION 'Sort Order cannot be between % and %',
checkit.minimum, checkit.maximum;
        EXIT;
     END IF;
  END IF;
  RETURN NULL;
END;

--
Robert