Index: /lib/wpsg_calculation.class.php
===================================================================
--- /lib/wpsg_calculation.class.php	(revision 7486)
+++ /lib/wpsg_calculation.class.php	(revision 7487)
@@ -163,5 +163,5 @@
 		 * 
 		 */
-		public function addVoucher($set, $bruttonetto, $tax_key, $amount = 1, $code = false, $id = false, $order_voucher_id) {
+		public function addVoucher($set, $bruttonetto, $tax_key, $amount = 1, $code = false, $id = false, $order_voucher_id = 0) {
 		 
 			$tax_key = $this->normalizeTaxKey($tax_key);