CodeIgniter - upload directory is invalid

I again need your help!

My codeigniter upload function doesn't work correctly, it's returning the message:"invalid upload path".

My form is a customer register form, with personal data and a field to upload personal files, if form validation is true does the upload.

Follows part of my controller code that is responsible for upload:

            //MAKE THE UPLOAD DIR BASE WITH PREVIOUS DEFINED NAME
            mkdir("./uploads/$dirname", 0777);
            //UPLOAD CUSTOMERS FILES
            $config['upload_path']   = "./uploads/$dirname";
            $config['allowed_types'] = 'gif|jpg|png|pdf';
            $config['max_size']      = 2048;
            $config['max_width']     = 1920;
            $config['max_height']    = 1280;

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

            if (!$this->upload->do_upload('userfile')) {
                $error = array('error' => $this->upload->display_errors());
                //SET SESSION MESSAGE FOR THE USER
                $this->session->set_flashdata('upload',$error);
            } else {
                $data = array('upload_data' => $this->upload->data());
                //SET SESSION MESSAGE FOR THE USER
                $this->session->set_flashdata('upload','Upload success!');
            }

My view return success to the data in the database and error to upload.

Below my directory structure:

web_administration
    |
    |-application
    |-src
    |-uploads
        |
        |-customer_directory
    |
    |-user_guide