Yii Simple RBAC Error - php

Question

I just a newbie in Yii. I have read http://www.yiiframework.com/wiki/328/simple-rbac/ and followed all instructions there, but I had error User.roles is not defined when I tried to login. Here is my UserIdentity.php
<?php
class UserIdentity extends CUserIdentity
{
private $_id;
public function authenticate()
{
$user = User::model()->findByAttributes(array
('username'=>$this->username));
if($user===null){
$this->errorCode=self::ERROR_USERNAME_INVALID;
}
else{
if($user->password!==$user->encrypt($this->password)){
$this->errorCode=self::ERROR_PASSWORD_INVALID;
}
else{
$this->_id = $user->username;
$this->setState('roles', $user->roles);
$this->errorCode=self::ERROR_NONE;
}
}
return !$this->errorCode;
}
public function getId(){
return $this->_id;
}
}
And then EWebUser.php
<?php
class EWebUser extends CWebUser
{
public function checkAccess($operation, $params=array())
{
if (empty($this->id)) {
// Not identified => no rights
return false;
}
$role = $this->getState("roles");
if ($role === 'admin') {
return true; // admin role has access to everything
}
// allow access if the operation request is the current user's role
return ($operation === $role);
}
}
At last accessRules method in UserController.php
public function accessRules()
{
.....
return array(
array('allow', // allow admin user to perform 'admin' and 'delete' actions
'actions'=>array('admin','delete'),
//'users'=>array('admin'),
'roles'=>array('admin'),
.....
);
}
I hope anyone can help me solve this problwm, thank you very much