Connection of SQL SERVER 2012 with Codeigniter

Hello everyone, I am developing a system with CI, Mysql and Sql Server 2012, I am configuring in php 5.6.30 and I put all the exemptions in php.ini and nothing I get this error when I pick it up

and that's in my databse, php

$db['sqlserver'] = array(
'dsn' => '',
'hostname' => '10.5.50.28',
'username' => 'sa',
'password' => 'SQLserver2012',
'database' => 'BD_UGEL_IMAGING',
'dbdriver' => 'sqlsrv',
'dbprefix' => '',
'pconnect' => FALSE,
'db_debug' => (ENVIRONMENT !== 'production'),
'cache_on' => FALSE,
'cachedir' => '',
'char_set' => 'utf8',
'dbcollat' => 'utf8_general_ci',
'swap_pre' => '',
'encrypt' => FALSE,
'compress' => FALSE,
'stricton' => FALSE,
'failover' => array(),
'save_queries' => TRUE

);

and this is my modal

class caja_model extends CI_Model {

function __construct() {
    parent::__construct();
    $this->db_caja = $this->load->database('caja', TRUE);
    $this->db_resoluciones = $this->load->database('resoluciones', TRUE);
    $this->db_sqlserver = $this->load->database('sqlserver', TRUE);
}

The funny thing is my partner's machine if he raises