ADOconnection to Oracle 8.0, failed to retrieve tables


I'm accessing Oracle database using Delphi 6.0 ADO component which
connection 'test' is ok, but when trying to get the tablename property of
ADOTable1 (after connecting to ADOConnection1) I got an error message "Data
provider or other service return an E-FAIL status'

Anybody knows what is wrong ?

Thanks in advance for any advise.