Linked Sever with Oracle Oledb provider query failed!

I'v setuped a Oracle8.16 linked server througth oracle oledb provider:
OraOLEDB.Oracle. When I use this linked server to get data, SqlServer
gave the following error message:
"OLE DB provider 'OraOLEDB.Oracle' reported an error. The provider did not give any information about the error."
But when I change the OraOLEDB.Oracle provider to MSDAORA,
none error occured!
Can somebody pls. guide me to resolve the issue?
many thanks in advance?Here is the code I used to create a linked server and then select data
set nocount on
go
declare @.server sysname
declare @.userid varchar(10)
declare @.pswd varchar(10)

set @.server = 'ATHENA_ORA'
set @.userid = 'system'
set @.pswd= 'manager'

exec sp_dropserver @.server = @.server , @.droplogins ='droplogins'

EXEC sp_addlinkedserver
@.server = @.server,
@.srvproduct = 'Oracle',
@.provider = 'MSDAORA',
@.datasrc = 'DBS_Athena'

exec sp_addlinkedsrvlogin @.server, 'FALSE', NULL, @.userid, @.pswd

exec sp_linkedservers
GO

SELECT * FROM ATHENA_ORA..SCOTT.DEPT

A couple of points, @.datasrc = 'DBS_Athena', 'DBS_Athena' is defined in my TNSNAMES.ORA, which was done by using Net8 or SQL*Net. Also I had to put the schema.tablename in uppercase. SELECT * FROM ATHENA_ORA..SCOTT.DEPT worked, but SELECT * FROM ATHENA_ORA..SCOTT.dept or SELECT * FROM ATHENA_ORA..scott.DEPT did not work.