Different versions of SQL Native Client in SQL Server 2008 R2

I have this error when I try to connect from a Server called: AplicationServer1 to another server in the same domain Kobl, called DatabaseServer1

SQLSTATE[28000]: [Microsoft][SQL Server Native Client 11.0][SQL Server]Login failed for user 'KOBL\kobladmin'.

The first strange thing is in DatabaseServer1 has Sql Server 2008 R2 with Sql Native Client 10.0 and I dont know why appear 11.0 versión in the above line when I try to connect to DatabaseServer in browser.

I'm using on side AplicationServer1:

• PHP 5.4
• IIS 7

DatabaseServer1:

• Sql Server 2008 R2

I'm use that code to make connection:

config.php

<?php
define ("DB_USER","KOBL\kobladmin");
define ("DB_PASS","AdminKobl");
define ("DSN","sqlsrv:server=databasebserver1.kobl.com;database=kobl_system");
?>

connect.php

<?php
require 'config.php';

class DB_Connect {

private static $_instance;

//Connecting to database
public function &pdo_connect() {
    if(!self::$_instance) {
        try{
            self::$_instance = new PDO(DSN,DB_USER, DB_PASS);
            self::$_instance->setAttribute(PDO::ATTR_PERSISTENT, true);
            self::$_instance->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        } catch (PDOException $ex) {
            die("PDO Connection error: ".$ex->getMessage()."<br/>");
        }
    }
    return self::$_instance;
}

private function __construct() {
}

private function __clone() {
}
}
?>

Credential to connect Sql Server is the same that Windows Authentication.

Note: Names of domain, user and password are fake (I put that because sometimes say me "You couldn't put real data of your database connection".