why models are not loading in autoload

You're a bit skimpy on details supporting your claim that models aren't autoloaded.

application/config/autoload.php ...
$autoload['model'] = array('customer');

tells CodeIgniter to look for the class "Customer" inside application/models/Customer.php

Note the UCfirst convention.

i knew it  but some model in autoload it will not work and the same model will work when i call it in controller and some are vice versa
why this has been happen and give me a correct link  to download the php and codeigniter should perfectly in that