Index: includes/cache.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/cache.inc,v
retrieving revision 1.49
diff -u -p -r1.49 cache.inc
--- includes/cache.inc	7 Oct 2010 17:44:53 -0000	1.49
+++ includes/cache.inc	3 Nov 2010 19:20:32 -0000
@@ -389,7 +389,7 @@ class DrupalDatabaseCache implements Dru
     // timer. The cache variable is loaded into the $user object by _drupal_session_read()
     // in session.inc. If the data is permanent or we're not enforcing a minimum
     // cache lifetime always return the cached data.
-    if ($cache->expire != CACHE_PERMANENT && variable_get('cache_lifetime', 0) && $user->cache > $cache->created) {
+    if ($cache->expire != CACHE_PERMANENT && variable_get('cache_lifetime', 0) && isset($user->cache) && $user->cache > $cache->created) {
       // This cache data is too old and thus not valid for us, ignore it.
       return FALSE;
     }