If you change your WordPress/WordPress mu table prefix (and thus, renamed the tables too) and you have a bbPress integrated with it, chances are your bbPress will lose its connection with WordPress since the configuration is not in bb-config.php. You’ll need to update the meta tables, too through mysql or phpmyadmin. Here’s the update query.
SET meta_value = 'wpmu_'
WHERE meta_key = 'wp_table_prefix';
That’s of course considering your bbPress table is bb_meta and the new prefix for WordPress/WordPress mu is wpmu.