Index: includes/cache.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/cache.inc,v
retrieving revision 1.17.2.4
diff -u -p -r1.17.2.4 cache.inc
--- includes/cache.inc	16 Dec 2009 17:30:00 -0000	1.17.2.4
+++ includes/cache.inc	28 Jan 2010 19:25:32 -0000
@@ -39,7 +39,7 @@ function cache_get($cid, $table = 'cache
     // cache timer. The cache variable is loaded into the $user object by
     // sess_read() in session.inc.
     else {
-      if ($user->cache > $cache->created) {
+      if (isset($user->cache) && $user->cache > $cache->created) {
         // This cache data is too old and thus not valid for us, ignore it.
         return 0;
       }