file upload controller

[eluser]KrizzAngel[/eluser]
i cant get it to work pls help.. here's my controller:
it keeps on saying "You did not select a file to upload."

class admin extends Controller {

function admin(){
parent::Controller();
$this->load->helper('form');
}

function upload() {
$baseLoc= base_url();
$config['upload_path'] = $baseLoc."assets/Lessons/";
$config['allowed_types'] = 'swf|flv';
$chap = $this->input->post('chapnum');
$less= $this->input->post('lessnum');
$config['file_name'] = "lesson_".$chap;

$this->load->library('upload', $config);
if ( ! $this->upload->do_upload('file'))
{
echo $this->upload->display_errors();
}
else
{
echo $this->upload->data();
}
}
}

and my view page:

<? echo form_open_multipart('admin/upload'); ?>
<input type="hidden" name="chapnum" value="<? echo $chapnumber; ?>" />
<input type="hidden" name="lessnum" value="<? echo $lessNum; ?>" />
<input type="file" name="vid" /><br />
<input type="submit" value="Next" />