Index: /Users/andrew/Documents/workspace/pinchin/sites/default/modules/signup/signup.module
===================================================================
--- signup.module	(revision 99)
+++ signup.module	(working copy)
@@ -300,7 +300,7 @@
   global $user;
 
   // Load the node if it already exists.
-  if (isset($form['nid']['#value'])) {
+  if (isset($form['nid']['#value']) && !empty($form['nid']['#value'])) {
     $node = node_load($form['nid']['#value']);
   }
   else {