To troubleshoot, make the following changes:
1) Change UE so it will not redirect. Change:
$GoToPage = "showcase_thanks.php";
$GoToPage = "";
2) turn on error reporting, add the following code at line 1:
3) Add the debug info binding to the body of the page. Go to the bindings panel and expand the WA UPloaded File Global Status bind group and add the debug info binding to the page.
4) dump the $_Files collection.
Near the closing </body> tag add the following code:
<?php var_dump($_FILES); ?>
after testing, this will show any errors occurring, the debug info from file upload and the contents of the $_FILES collection, post those details back please.