try help me with this error

[eluser]ejanmapet[/eluser]
i have try 2 follow login form tutorial..but i've got this error

Fatal error: Class 'Base_Model' not found in C:\wamp\www\try\system\application\models\Users_model.php on line 3

and this is the code i'm using in model

this is user_model file

<?php if (!defined('BASEPATH')) exit('No direct script access allowed');

class Users_model extends Base_Model
{
function Users_model()
{
parent::Base_model('users');
}
}
?>

this is base_model file

class Base_model extends Model //required by all models
{
var $table, $resultset, $select;

function Base_model($table = NULL)
{
parent::Model();
$this->table = $table;
$this->resultset = array();
$this->select = '*';

log_message('debug', "Base_model initialised as {$this->table}");
}

can i get some idea y i got this bug..really appreciate...thanks..