Error occured in cake php

Error: Class ‘User_activity_log’ not found .

**this error coming into helper . code are given bellow **

** function getUserSessionTime($id = null)**
** {**
** App::import(“Model”, “User_activity_log”); **
** $Model = new User_activity_log(); **
** //$Model =& ClassRegistry::getObject(‘User_activity_log’); **
** $userData = $Model->find(‘all’,array(‘conditions’=>array(‘user_id’=>$id)));**


** if(!empty($userData))**
** {**
** return $userData;**
** } **
** else**
** {**
** return ‘No Data Found’;**
** }**
** }**

If you want us to help you, you should do more than just ugly paste the error…
Check if the import works, check the name of the class, …