Call get_instance() in Hook Class

Hi everybody,

In my application I try to call get_instance() in pre_system hook class. But then error message appeared:

Code:

A PHP Error was encountered
Severity: Error
Message: Class 'CI_Controller' not found
Filename: core/CodeIgniter.php
Line Number: 366

that line refers to get_instance() function in core/CodeIgniter.php. After I check the pre_system hook called before the core/Controller.php included.

Any ideas how to solve this?