I think the issue may have just been a syntax problem. The code that I posted looks like it is missing a left parenthesis, in the file you posted there is one extra left parenthesis in the code. Try updating line 60 of WAUE_registration_3.php to be like this:
$MailBody = $MailBody . ((isset($_POST["UserNewsletter"]) && $_POST["UserNewsletter"] == '1')?"Yes":"No");
Please update this and give it a try, I think it should work after this.