'You did not select a file to upload' codeigniter - php

Question

I am trying to upload an image via codeigniter but constantly recieve the following message: 'You did not select a file to upload'.
I have viewed many SO answers on this but nothing has helped:
PHP config max File upload size: 2M (I tested with 0.5mb files)
Form is multipart
Website is on localhost
HTML:
<h3>Upload profile image</h3>
<div data-role="fieldcontainer">
<form action='do_upload_prof' method='post' enctype="multipart/form-data">
<input type="file" name='file'>
<input type='submit' value='upload' />
</form>
</div>
PHP Controller:
public function do_upload_prof() {
$config = array(
'upload_path' => "./profile_img/",
'allowed_types' => "gif|jpg|png|jpeg",
'overwrite' => TRUE,
'max_size' => "4048000",
'max_height' => "768",
'max_width' => "1024"
);
$this->load->library('upload', $config);
if ($this->upload->do_upload('file')) {
$data = array(
'upload_data' => $this->upload->data()
);
$this->load->view('header');
$this->load->view('profile', $data);
$this->load->view('footer');
} else {
$error = array(
'error' => $this->upload->display_errors()
);
$this->load->view('header');
$this->load->view('profile', $error);
$this->load->view('footer');
}
}