--- C:/patch/Original/session.inc	Mon Feb 06 21:30:01 2012
+++ C:/patch/Modified/session.inc	Mon Feb 06 21:25:44 2012
@@ -172,7 +172,7 @@
 
     // For performance reasons, do not update the sessions table, unless
     // $_SESSION has changed or more than 180 has passed since the last update.
-    if ($is_changed || REQUEST_TIME - $user->timestamp > variable_get('session_write_interval', 180)) {
+    if ($is_changed || !isset($user->timestamp) || REQUEST_TIME - $user->timestamp > variable_get('session_write_interval', 180)) {
       // Either ssid or sid or both will be added from $key below.
       $fields = array(
         'uid' => $user->uid,