first off, leave the file name setting in the wizard as the default [FileName] instead of trying to bind to the file form element.
next add the following code at line 1 to turn on error reporting:
<?php
error_reporting(E_ALL);
ini_set('display_errors','on');
?>
then add this code after the body tag:
<?php echo WA_DFP_AllUploadsDebug(); ?>
back back the results after a test