OEM export job error

Hi to every one ... Please Help ME !!!
I'am neubie in Oracle ...
I installed Oracle 9i and the Oracle Enterprise Manager Consolle ( ver. 9.0.1.0.0). I'd like to manage 3 disctint oracle db with OEMC( in 3 different version one is 9.0.1.1.1, second is 8.1.6.1.0 and an 8.0.5.0.0 !!! yes I know is crazy) bye the way everthing works fine, I can start/shoutdown all dbs, manage security etc. I setup all credential for each dbs ( and I create the oracle user to post job on each nt server with privilege to read/write the tmp directory and oracle net directory, and on each db I logon as sys with sysdba privilegies). So the problem is that I can correctly run an export on 9i with no problems but when I submit a export job on 8.1.6.0 it fails with the following error :

Export: Release 8.1.6.1.0 - Production on Thu Mar 7 17:54:28 2002 (c) Copyright 1999 Oracle Corporation. All rights reserved.

EXP-00056: ORACLE error 12638 encountered
ORA-12638: Credential retrieval failed
EXP-00000: Export terminated unsuccessfully

I'm going to be crazy .... HELP ME PLEASE !!  

I haven't found no error/bugs on metalink !!

Bye
Fabio Received on Fri Mar 08 2002 - 02:37:03 CST