The problem is that your form is send via ajaxForm to upload_file.php and everything should work fine in this call returning the expected string. With this server response your callback function is called and here you call upload_file.php again without any parameters and render the result in the div, that is only "this works" . You should use the plugin like the following:
$('#insert_movie').ajaxForm({
success: function(response) {
$('#message').html(response);
}});