Trigger Error!

Hi!

I've postgresql 6.5.3 system and 50 tables, but i need to run  this
trigger: (the comments are in spanish :-) )

create function gen_req() returns opaque as '
    declare
     cantdisp int4;
     suma int4;
     cantprodsol int4;
     codereq int4;

   begin
    if int4ne(new.candisproter, old.candisproter) then
       select candisproter into cantdisp from proter
       where codproter=new.codproter;

       if not found then
          raise exception ''No hay datos de productos'';
       end if;

       select sum(stomin) into suma from almproterpt
       where codproter=new.codproter;

       if not found then
          raise exception ''No hay datos de Stocks minimos'';
       end if;

       cantprodsol := old.candisproter - new.candisproter;

       if int4le((cantdis - cantprodsol), suma) then
        select codreq from requisicion
        where fecsalreq=current_date;
  if not found then
           --se inserta la requisicion;
           insert into requisicion(fecsalreq,codest)
values(current_date,1);
         end if;
        --se repite la query pero asignando el valor;
        select codreq into codereq from requisicion
        where fecsalreq=current_date;
        --procedemos a insertar el detalle;
        insert into detallereq(codreq,codpt,canpt)
        values(codereq,new.codproter,cantprodsol);
       end if;
     end if;
     return new;
   end;
' language 'plpgsql';

create trigger gen_req_tg before update on proter for each row execute
procedure gen_req();

Well, the trigger is created, the trigger should intercepts the update
event in table 'proter' and  when  I reduce the 'candisproter' field to
specied value then, the trigger is fired. But.........

It isn't work, when I run the update operation, then, I give this error:

'There is no operator '=$' for types 'int4' and 'int4' you will either
have to retype this query using and explicit cast, or you will have
to define the operator using CREATE OPERATOR'

I don't understand  what's the meaning af this message, the types are
incorrect??  WHAT'S WRONG?????

thankx!!!