all looks correct. Does this return any errors when you test it?
add the following code just before the </body> tag and post bacj the output of this code after testing an upload.
POST:<br />
<pre><?php var_dump($_POST); ?></pre>
FILES:<br />
<pre><?php var_dump($_FILES); ?></pre>
<br />
<?php echo WA_DFP_AllUploadsDebug(); ?>