1) the ini_set code you have at line 25 - 28:
<?php
ini_set('memory_limit','500M');
?>
should be moved to line 1.
2) Just before that code block add this code block:
<?php
error_reporting(E_All);
ini_set('display_errors','on');
?>
3) change this line:
$WA_redirectURL = "Catalog_Insert.php";
to:
$WA_redirectURL = "";
4) Add this code just after the <body> tag:
<?php echo WA_DFP_AllUploadsDebug(); ?>
this will write debuging info to the screen, post back the results after trying to upload a file.