problem with using linked server

:) hello everybody, i am using oracle as linked derver to my sql server db...when i write the query to access data from linked server(oracle) iam getting error like this...iam helpless..pls give ur ideas..
my query is: SELECT * FROM EOPI..EOP.CONTRACT
and the error is
OLE DB provider 'OraOLEDB.Oracle' reported an error.
[OLE/DB provider returned message: ORA-12638: Credential retrieval failed]..

thax and regards
kiran
senior software engineer :cool:When querying by linked server you have to use openquery.

SELECT * FROM OPENQUERY(linkedservername,'SELECT * FROM pubs')