=== modified file 'uc_product/uc_product.module'
--- uc_product/uc_product.module	2010-11-23 15:23:43 +0000
+++ uc_product/uc_product.module	2010-11-23 16:18:22 +0000
@@ -1191,8 +1191,13 @@
  * Implement hook_uc_add_to_cart_data().
  */
 function uc_product_uc_add_to_cart_data($form_values) {
-  $node = node_load($form_values['nid']);
-  return array('shippable' => $node->shippable);
+  if (isset($form_values['nid'])) {
+    $node = node_load($form_values['nid']);
+    return array('shippable' => isset($node->shippable) ? $node->shippable : variable_get('uc_product_shippable_' . $node->type, 1));
+  }
+  else {
+    return array('shippable' => variable_get('uc_product_shippable_product', 1));
+  }
 }
 
 /**