Problem with extjs and codeigniter

[eluser]Unknown[/eluser]
I try to use extjs and codeigniter make a form submit example.But if I type the error username and passwd and then I press the submit button,the firebug occur an error,I do not know how to fix it ,can anynoe help me
this is my code:

Code:

<?php
    class Login extends Controller
    {
        public function __construct()
        {
            parent::Controller();
            $this->load->model('drugdb','use');
            $this->sets        = parse_ini_file("./extends/global.ini");
            $this->local    = parse_ini_file($this->sets['rela'].$this->sets['ini'].__CLASS__.$this->sets['type'],true);
        }
        
        public function index()
        {
            $this->load->library('validation');
            $this->load->helper('form');
            $this->load->helper('cookie');
            $data['title']        = $this->local[__FUNCTION__]['title'];
            $data['error']        = '';
            $data['rootPath']    = $this->local[__CLASS__]['rootPath'];
            $username    = $this->input->post('username');
            $passwd        = $this->input->post('passwd');
            $rules['username']    = 'callback_username_check';
            $this->validation->set_rules($rules);
            if ($this->validation->run()    == false)
            {
                $this->load->view($this->sets['viewPath'].'/'.$this->local[__CLASS__]['viewFloder'].'/'.$this->local[__FUNCTION__]['viewName'],$data);
            }
            else
            {
                set_cookie('username',$username,0);
                set_cookie('logged',true,0);
                redirect('drugindex');
            }
        }
        
        public function username_check($str)
        {
            $passwd        = $this->input->post('passwd');
            $count        = $this->use->get_count('admin',array('username'=>$str,'passwd'=>md5($passwd)));
            if ($count >0)
                return true;
            else
            {
                $this->validation->set_message('username_check','<span class="highlight">login error</span>');
                return false;
            }
        }
    }
?&gt;

psorry about my english