working with models

[eluser]karltingume2007[/eluser]
please, i urgently need help with working with models. i am still quite new in codeigniter and i have this problem at the level of working with models. on loading my model, the code written in that class is brought to the screen followed by the error message:- Fatal error: Class 'Addressbook_model' not found in C:\Program Files\EasyPHP 2.0b1\www\sample\system\core\Loader.php on line 303. am sorry to say this, but to tell you all the truth, i need help and really quickly. thank you