I'm getting many Fatal errors like this in Wordpress 3.6.1, multisite with Buddypress:
PHP Fatal error: Call to a member function suppress_errors() on a non-object in /myblog/wproot/wp-includes/option.php on
The non-object referred to is the global value $wpdb, in the line:
$suppress = $wpdb->suppress_errors();
which is in the function wp_load_alloptions()
Any ideas why $wpdb would not be set, and if there is anything to be done to remedy this? Sorry I don't have any more useful on this, the errors are isolated and don't show a stack trace.