File upload error

hi , i have an error with file upload :

The original file is not a valid file


when i leave empty the file field


this is my code : 

PHP Code:

                //recupero le informazioni del file
                $img = $this->request->getFile('immagine');



                if($img){

                    //lo trasferisco nella cartella uploads
                    if($img->move(FCPATH . '/uploades/images/foto_mezzi')){

                
                        $post['immagine'] = $img->getName(); 

                            $res= $mezzi_model->save($post);