Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 136)
+++ wp-includes/pluggable.php	(working copy)
@@ -783,7 +783,7 @@
 function is_user_logged_in() {
 	$user = wp_get_current_user();
 
-	if ( $user->id == 0 )
+	if ( !isset($user) || $user->id == 0 )
 		return false;
 
 	return true;
@@ -1334,7 +1334,13 @@
  */
 function wp_create_nonce($action = -1) {
 	$user = wp_get_current_user();
+
+    if (isset($user)) {
 	$uid = (int) $user->id;
+    }
+    else {
+        $uid = 0;
+    }
 
 	$i = wp_nonce_tick();