我的codeigniter程序有问题

i have build some program with Codeigniter 3, but i have a problem when i try to update setting the variable of input is Undefined.

When i try to get site_title input with $_POST['site_title'], i see this error:

and when i try to get with $this->input->post('site_title'), error: Access to my web was denied.

but in a local server, all proses running well. please help me!! thanks