Should use tp_account_manager_dup()

 /* the daemon is used to communicate via DBus */
 daemon = tp_dbus_daemon_dup(&error);

 if (daemon == NULL)
 {
  g_debug("Cannot create DBus daemon: %s\n", error->message);
  g_error_free(error);
  return;
 }

 priv->manager = TP_ACCOUNT_MANAGER (g_object_new (TP_TYPE_ACCOUNT_MANAGER,
  "dbus-daemon", daemon,
  "dbus-connection", ((TpProxy *) daemon)->dbus_connection,
  "bus-name", "org.freedesktop.Telepathy.AccountManager",
  "object-path", "/org/freedesktop/Telepathy/AccountManager",
  NULL));

Any reason to not use tp_account_manager_dup()? That would make this code much simpler.