diff -uPr uc_varprice-fixed.module uc_varprice.module
--- uc_varprice-fixed.module    2011-09-12 15:21:32.000000000 +1000
+++ uc_varprice.module  2011-09-12 15:13:54.000000000 +1000
@@ -69,11 +69,14 @@
     for ($i = 0, $j = count(uc_cart_get_contents()); $i < $j; $i++) {
       $data = unserialize($form['items'][$i]['data']['#value']);

-      // If this item has a quantity restriction on it...
-      if ($data['varprice'] > 0) {
-        $form['items'][$i]['qty']['#type'] = 'value';
-        $form['items'][$i]['qty']['#theme'] = 'varprice_qty';
-      }
+         if (array_key_exists('varprice', $data))
+         {
+                 // If this item has a quantity restriction on it...
+                 if ($data['varprice'] > 0) {
+                       $form['items'][$i]['qty']['#type'] = 'value';
+                       $form['items'][$i]['qty']['#theme'] = 'varprice_qty';
+                 }
+         }
     }
   }