Site is down: wordpress database error

Hi
Site its down and Im getting this error:
[04-Jan-2013 15:56:29 UTC] WordPress database error MySQL server has gone away for query SELECT meta_value FROM wp_sitemeta WHERE meta_key = 'ms_files_rewriting' AND site_id = 1 made by require('wp-blog-header.php'), require_once('wp-load.php'), require_once('wp-config.php'), require_once('wp-settings.php'), include_once('/plugins/buddypress-activity-plus/bpfb.php'), wp_upload_dir, get_site_option

Help will be appreciated.