[otrs] help with Oracle connection

I am getting a Message: Error while trying to retrieve text for error ORA-12541 (DBD ERROR: OCIServerAttach) error when trying to connect to a Oracle 9 database. Despite the error message, the listener is running, and I can connect to the OTRS user with other third party apps( like TOAD ). I suspect perhaps some kind of environment settings not correct? I need to understand more about how OTRS makes a connection to a Oracle database so I can investigate further. Any pointers?