diff -urN wordpress_213/wp-includes/cache.php wordpress_213.hk/wp-includes/cache.php
--- wordpress_213/wp-includes/cache.php	2007-02-01 11:03:34.000000000 +0100
+++ wordpress_213.hk/wp-includes/cache.php	2007-04-19 19:29:31.000000000 +0200
@@ -29,6 +29,10 @@
 function wp_cache_get($id, $flag = '') {
 	global $wp_object_cache;
 
+	if (!is_object($wp_object_cache)) {
+		$wp_object_cache = new WP_Object_Cache();
+	}
+
 	return $wp_object_cache->get($id, $flag);
 }
 
@@ -188,6 +192,10 @@
 	function load_group_from_db($group) {
 		global $wpdb;
 
+		if (!is_object($wpdb)) {
+			$wpdb = new wpdb(DB_USER, DB_PASSWORD, DB_NAME, DB_HOST);
+		}
+
 		if ('category' == $group) {
 			$this->cache['category'] = array ();
 			if ($dogs = $wpdb->get_results("SELECT * FROM $wpdb->categories")) {