access helper function inside controller

[eluser]ranjitbd[/eluser]
[quote author="ranjitbd" date="1260807351"][code]
// when i put the same method inside my customized library
// it shows the following error in that same line number 103
// that line:
$this->session->set_userdata($menu_data);

Fatal error: Call to a member function set_userdata() on a non-object in C:\xampp\htdocs\travelmartbd\appl