Index: /lib/wpsg_calculation.class.php
===================================================================
--- /lib/wpsg_calculation.class.php	(revision 7210)
+++ /lib/wpsg_calculation.class.php	(revision 7211)
@@ -788,5 +788,6 @@
 				else {
 					
-					$this->arCalculation['tax'][$tax_key]['part'] = $tax[$bruttonetto] / $sum;
+					if ($sum <= 0) $this->arCalculation['tax'][$tax_key]['part'] = 0;
+					else $this->arCalculation['tax'][$tax_key]['part'] = $tax[$bruttonetto] / $sum;
 					
 				}