avahi daemon unable to start after upgrade to Jaunty

I just upgraded to Jaunty skipping a couple of releases, probably from Gutsy or Hardy. The system no longer broadcasts its IP address using the Bonjour protocol, because the daemon doesn't start.

# /etc/init.d/avahi-daemon restart
 * Restarting Avahi mDNS/DNS-SD Daemon avahi-daemon [fail]

==> /var/log/daemon.log <==
Feb 10 11:26:22 *** avahi-daemon[11948]: Found user 'avahi' (UID 115) and group 'avahi' (GID 118).
Feb 10 11:26:22 *** avahi-daemon[11948]: Successfully dropped root privileges.
Feb 10 11:26:22 *** avahi-daemon[11948]: avahi-daemon 0.6.23 starting up.
Feb 10 11:26:22 *** avahi-daemon[11948]: dbus_bus_get_private(): Failed to connect to socket /var/run/dbus/system_bus_socket: No such file or directory
Feb 10 11:26:22 *** avahi-daemon[11948]: WARNING: Failed to contact D-Bus daemon.

# lsb_release -rd
Description: Ubuntu 9.04
Release: 9.04

# apt-cache policy avahi-daemon
avahi-daemon:
  Instalados: 0.6.23-4ubuntu4
  Candidato: 0.6.23-4ubuntu4
  Tabla de versión:
 *** 0.6.23-4ubuntu4 0
        500 http://us.archive.ubuntu.com jaunty/main Packages
        100 /var/lib/dpkg/status
     0.6.23-2ubuntu2.1 0
        500 http://security.ubuntu.com intrepid-security/main Packages