在codeigniter（php）中调用控制器时出错？

I made a website in codeigniter . it is working fine on local host and on the live server it is opening the default controller normally but when i m tring to call other controller then i m getting error of No input file specified. everything is working fine on local host .

class Contact_us extends CI_Controller {

public function index()

   {

       echo  $data["header"] = $this->load->view('header');

        //$this->load->view('index',$data); 

    }   

}

I am calling my controller like mysitename/index.php/contact_us

it works with change in htaccess file like

 DirectoryIndex index.php
 RewriteEngine on

 RewriteCond %{REQUEST_FILENAME} !-f
 RewriteCond %{REQUEST_FILENAME} !-d
 RewriteRule ^(.*)$ ./index.php?$1 [L,QSA]

and put $config['index_page'] = ""; in the config file so now my site url becomes like mysitename/contact_us