Are you using the datastore (check in your config.php):
PHP Code:
// ****** DATASTORE CACHE CONFIGURATION *****
// Here you can configure different methods for caching datastore items.
// vB_Datastore_Filecache - to use includes/datastore/datastore_cache.php
// vB_Datastore_APC - to use APC
// vB_Datastore_XCache - to use XCache
// vB_Datastore_Memcached - to use a Memcache server, more configuration below
$config['Datastore']['class'] = 'vB_Datastore_Filecache';
If so, did you make sure the datastore folder is chmod to 777? Is the datastore_cache file being updated?