store the error message in a session variable. Add the following code just before the Insert:
<?php
if(!session_id()) session_start();
if($_SERVER["REQUEST_METHOD"] == "POST"){
$_SESSION['dfpError'] = $WA_DFP_UploadStatus["WA_UploadResult1"]["errorMessage"];
}
?>
On the page add this to show the error:
<?php echo(isset($_SESSION['dfpError'])?$_SESSION['dfpError']:""); ?>