custom helper file isn't loading codeigniter

[eluser]Xeroxeen[/eluser]
Hi,

I created a custom helper in codeigniter.And placed it in the system/helpers folder.My file name was "customhelper_helper.php".Then i loaded it in my controller this way."$this->load->helper('customhelper');".After that i called the function inside the helper file.But it's not working.Why is that?Plz help guys...