pagination doesn't work

Hi guys.
what part is wrong? here is my code. and here is error

A PHP Error was encountered

Severity: Notice

Message: Undefined index: username

Filename: users/index.php

Line Number: 45

controller:

PHP Code:

public function index(){
        $this->load->library('pagination');
        $this->load->model('user_model');

        $config['base_url'] = base_url().'index.php/admin/index.php/user/page';
        $config['total_rows'] = $this->user_model->get_users_count();
        $config['per_page'] = 1;
        $config['uri_segment'] = 4;
        $page = ($this->uri->segment(4))?$this->uri->segment(4):0;
        $config['first_link'] = 'First';
        $config['last_link'] = 'Last';
        $this->pagination->initialize($config);
        
        $data['result'] = $this->user_model->get_all($config['per_page'], $page);
        $data['link'] = $this->pagination->create_links();

        $this->template->load('users/index', array('users' => $data));
    } 


Model:

PHP Code:

public function get_all($limit,$start){
        return $this->db->get('users', $limit, $start)->result_array();
    }

    public function get_users_count(){
        return $this->db->count_all('users');
    } 


view:

PHP Code:

<?php foreach($users as $key => $value):?>
                            <tr>
                                <td><?=$value['username']; ?></td>
                                <td><?=$value['email'];?></td>
                                <td><?=$value['status'];?></td>
                                <td><?=$value['access'];?></td>
                            </tr>
                            <?php endforeach; ?>

                            <?php
                                echo $pagination;
                            ?>