Php – ODBC Connection with IBM DB2 using PHP 5.1.6

I'm using CentOS release 5.6 (Final) with PHP 5.1.6 (cli) (built: Feb 2 2012 18:24:47).
I need to connect with a DB2 database server in same local network.
Db2 version is V5R3.
I have installed iSeriesAccess client as well as unixODBC.

My odbc.ini configuration:

[iSeries Access ODBC Driver]
Description             = iSeries Access for Linux ODBC Driver
Driver          = /opt/ibm/iSeriesAccess/lib/libcwbodbc.so
Setup           = /opt/ibm/iSeriesAccess/lib/libcwbodbcs.so
NOTE1           = If using unixODBC 2.2.11 or later and you want the 32 and 64-bit ODBC drivers to share DSN's,
NOTE2           = the following Driver64/Setup64 keywords will provide that support.
Driver64                = /opt/ibm/iSeriesAccess/lib64/libcwbodbc.so
Setup64         = /opt/ibm/iSeriesAccess/lib64/libcwbodbcs.so
Threading               = 2
DontDLClose             = 1

UsageCount              = 1

i'm running the following code:

<?php
$database = 'dbname';
$server = 'local_ip';
$user = 'username';
$password = 'password';
$driver = 'iSeries Access ODBC Driver';



$conn = odbc_connect("Driver={iSeries Access ODBC Driver};Server=$server;Database=$database;", $user, $password);
if (!$conn......)

I'm getting the following error message:
"[unixODBC][IBM][System i Access ODBC Driver]Missing system name needed for connection.Error!"

Is there anything I'm missing? your suggestions are welcome.