Linked Server Trigger Problem

Hi All!

My problem is that I created a linked server named RETAIL in SQL SERVER 2005 for Oracle db.

I can insert, delete, select, update datas from oracle db.like this:

SELECT * FROM RETAIL..USERNAME.TABLE1;

SELECT * FROM OPENQUERY(RETAIL,'SELECT * FROM TABLE1');

INSERT INTO RETAIL..USERNAME. TABLE1 VALUES (...);

UPDATE RETAIL..USERNAME.TABLE1 SET FIELD1= 'DENEME ';

DELETE FROM RETAIL..USERNAME.TABLE1 WHERE..

But when I use insert, update, delete statements for ORACLE DB in SQL SERVER TRIGGER trigger is created successfully but when it begins to run gives error like this:

OLE DB provider "MSDAORA" for linked server "RETAIL" returned message "ORA-01041:internal error. hostdef extension doesn"t exist

My Trigger is this:

CREATE TRIGGER REYON ON STOK_REYONLARI AFTER INSERT
AS  
DECLARE 
@RECNO INT

BEGIN  

SET @RECNO =(SELECT MAX(RYN_recNO) FROM STOK_REYONLARI)

INSERT INTO RETAIL..USERNAME.TABLE1 VALUES(@RECNO, 'I', 'STOK_REYONLARI')

END  

How can I fix this problem.