codeigniter can't upload picture to folder

I need help to upload picture in folder. Here's the thing, I have tested before and it worked. After a while I test this again and boom it doesn't work. I really can't think straight here, please help!

my view :

<?php 
        echo form_open_multipart("adminFolder/admin/insert_picture");

        echo form_upload("userfile", "Gambar Picture");

        echo form_submit("input_picture", "Input now !!!");

        ?>

my controller :

public function insert_picture(){
        $this->model_get->doUpload();
    }

my model :

function doUpload(){
        $path = './assets/images/';
        chmod($path, 0777);

        $config['upload_path'] = $path; 
        $config['allowed_types'] = 'gif|jpg|png|jpeg'; 
        $config['max_size'] = '6000'; 
        $config['max_width']  = '1024';
        $config['max_height']  = '768'; 
        $config['overwrite'] = TRUE;

        $this->load->library("upload", $config);

        if(!$this->upload->do_upload()){
            redirect("adminFolder/admin/insertPicture");
        }else{

            redirect("adminFolder/admin/adminPic");
        }


    }