I get "Invalid argument supplied" message in group forums page.

Suddenly on group forums page url, I start receiving below message.

Warning: Invalid argument supplied for foreach() in /home/wp-content/db.php on line 284

line 284 of db.php states:
foreach ( $db_servers[$query_data['dataset']] as $server ) {

I updated Multi-db by replacing the db.php with the new one. Did I forget something?