Undefined method.

[eluser]Mirge[/eluser]
You named the file register.php - change your class name to Register (or change your filename to register_model.php).

They're not consistent. For example, it SHOULD appear like this:

filename: register.php
class: class Register extends CI_Model { ... }
load: $this->load->model('register');
call: $this->register->create();