Problem with delete trigger

Hi! I've tried a trigger as: create trigger "informix".deleteoperations delete on "informix".operaciones referencing old as pre for each row ( execute procedure "informix".update_operations_balance(pre.cuentaorigen ,pre.cuentanum ,pre.cuentadc ,pre.idproducto ,pre.idoperacion,(pre.importe * -1.0000000000000000 ) ,pre.idtipoorden )); create procedure update_operations_balance(ctaorigen varchar(3),ctanum varchar(9), ctadc varchar(2), aidproducto varchar(12),aidoperacion int,aimp float,aidtipoorden varchar(10)) define impsigno float; if (aidproducto=='0') then select importe_segun_clase(clase,signo, aimp) into impsigno from tiposordenes where idtipoorden=aidtipoorden; update operations set saldo=saldo+impsigno where cuentaorigen=ctaorigen and cuentanum=ctanum and cuentadc=ctadc and idproducto=aidproducto and idoperacion>aidoperacion; end if end procedure When I run this code, I obtain the message error: SQL Error (-747): Table or column matches object referenced in triggering statement Can you help me?