File Upload error

[eluser]hrg.vincent[/eluser]
[quote author="CroNiX" date="1393562007"]You need to tell do_upload() the name of your file input.[/quote]

I've changed to code to below, but still the same issue, already added the name of input

Code:

if (!$this->upload->do_upload('flex_file')){
$error = array('error' => $this->upload->display_errors());
var_dump($error);  
}
else{
$data = array('upload_data' => $this->upload->data('flex_file'));
var_dump($data);
}