looks correct.
to troubleshoot, add the following code at line 1:
<?php
error_reporting(E_ALL);
ini_set('disaplay_errors','on');
?>
then open the bindings panel, and expand the WA Uploaded files binding group and add the debug info binding to your page
and add this code just before the </body> tag:
<?php
echo("POST:<pre>");
var_dump($_POST);
echo("</pre>");
echo("FILES:<pre>");
var_dump($_FILES);
echo("</pre>");
?>
post back the results after testing the upload. This will give us details about the upload to tell what may be going wrong.