perhaps the host has turned off the $_SERVER["HTTP_REFERER"] variable, find the following code on the confirm.php page
<?php
}
} //end paypal gateway
else if (($_SERVER["REQUEST_METHOD"] == "POST") && (isset($_SERVER["HTTP_REFERER"]) && strpos(urldecode($_SERVER["HTTP_REFERER"]), urldecode($_SERVER["SERVER_NAME"].$_SERVER["PHP_SELF"])) > 0) && isset($_POST)) {
$WA_Store_Cart->redirStr = "checkout_success.php";
}
?>
and change it to:
<?php
}
} //end paypal gateway
else if (isset($_POST["Submit_order"])) {
$WA_Store_Cart->redirStr = "checkout_success.php";
}
?>
if that does not work, add the following at line 1 to see if a php error is occurring:
<?php
error_reporting(E_ALL);
ini_set('display_errors','on');
?>