AutoLoad: can not load 3 library

[eluser]Unknown[/eluser]
auto load config:
$autoload['libraries'] = array('pagecontent', 'database', 'checkpermission');

Code:

class MyClass extends Controller{
  function MyClass() {
    parent:: Controller();
  }
  function myfunc() {
    $param = '1|1|1|1';
    $this->checkpermission->permit($param);  
  }
}

I call $this->checkpermission in class Myclass
Error:
Unknow MyClass::$checkpermission

Plz help!