Index: uc_node_checkout.module
===================================================================
--- uc_node_checkout.module	(revision 470)
+++ uc_node_checkout.module	(working copy)
@@ -555,7 +555,7 @@
     // any changed attribute options.
     case 'update':
       // Only save attributes if this node has not been checked out.
-      if (empty($node->uc_order_product_id)) {
+      if (empty($node->uc_order_product_id) && isset($node->attributes)) {
         $data = db_result(db_query("SELECT data FROM {uc_cart_products} WHERE data LIKE '%%\"node_checkout_nid\";i:%d;%%'", $node->nid));
 
         $data = unserialize($data);