Index: services.module
===================================================================
RCS file: /cvs/drupal-contrib/contributions/modules/services/services.module,v
retrieving revision 1.8.2.88.2.23
diff -u -p -r1.8.2.88.2.23 services.module
--- services.module	27 Oct 2010 20:40:09 -0000	1.8.2.88.2.23
+++ services.module	4 Dec 2010 15:36:44 -0000
@@ -863,7 +863,7 @@ function services_session_load($sessid) 
   sess_read($sessid);
 
   // Check if it really loaded the user.
-  if (isset($user->sid) && $user->sid != $sessid) {
+  if (!isset($user->sid) || isset($user->sid) && $user->sid != $sessid) {
     services_session_unload($backup);
     return NULL;
   }