bbPress.org

Are you using 0.8.3?

Try to patch with https://trac.bbpress.org/ticket/757

or

modify https://trac.bbpress.org/browser/trunk/bb-includes/db-mysqli.php#L56

to be

$this->$dbhname = @mysqli_connect( $server->host, $server->user, $server->pass, null, null, $server->port );