Still can't talk to the Oracle

I'm setting up a back end production system for a television show, and have been given space on a development server with PHP 4 and Oracle support compiled in (but not the OCI libraries). The Oracle admin have given me my user name (let's say ora_user), a TNS name (tns_name), and a password (ora_pass). So I write code as follows... if ($conn=ora_logon("ora_user@tns_name","ora_pass")) { echo "SUCCESS ! Connected to database\n"; } else { echo "Failed :-( Could not connect to database\n"; echo ora_errorcode($conn).": ".ora_error($conn)."<BR>"; } In response to this code, I get the following error: ORA-12154 "Supplied argument is not a valid Oracle-Connection/Cursor resource in ...." From reading php.net documentation on ora_logon, it seemed that maybe the ORACLE_HOME environment variable simply hadn't been set. I had the sys admins set it. And I still get the error. Any ideas from an experienced PHP/Oracle developer? Kristofer