401 Unauthorized OOPSes in the XMLRPC layer

Every few days, we get a bunch of OOPSes from the internal XMLRPC server,
related to getMessageDispositions(). The OOPSes seem random and I can't
figure out why we're getting them, let alone why only occasionally.

For the record, here are a few representative OOPSes.

OOPS-1205MMX1

OOPS-867S560

Note that the first OOPS is on the Mailman side of the XMLRPC interface. It's
telling us the server is getting a 401 Unauthorized, but unfortunately it does
not tell us where or why.

The second OOPS is on the server side and its even more cryptic.

Traceback (innermost last):
  Module zope.publisher.publish, line 138, in publish
    result = publication.callObject(request, object)
  Module canonical.launchpad.webapp.publication, line 342, in callObject
    return mapply(ob, request.getPositionalArguments(), request)
  Module zope.publisher.publish, line 113, in mapply
    return debug_call(object, args)
   - __traceback_info__: <security proxied zope.app.publisher.xmlrpc.metaconfigure.MailingListAPIView instance at 0xbbb1e10>
  Module zope.publisher.publish, line 119, in debug_call
    return object(*args)
  Module canonical.launchpad.xmlrpc.mailinglist, line 216, in getMessageDispositions
    for held_message in message_set.getHeldMessagesWithStatus(status):
  Module sqlobject.main, line 1674, in __iter__
    return conn.iterSelect(self)
  Module sqlobject.dbconnection, line 903, in iterSelect
    select, keepConnection=True)))
  Module sqlobject.dbconnection, line 809, in __init__
    self.cursor = rawconn.cursor()
  Module canonical.launchpad.webapp.adapter, line 250, in cursor
    return super(ReconnectingPsycopgConnection, self).cursor()
  Module psycopgda.adapter, line 388, in cursor
    return PsycopgCursor(self.conn.cursor(), self)
  Module canonical.launchpad.webapp.adapter, line 446, in cursor
    return LaunchpadCursor(self)
  Module canonical.launchpad.webapp.adapter, line 215, in __init__
    self._ensureCursor()
  Module canonical.launchpad.webapp.adapter, line 218, in _ensureCursor
    self.connection._ensureConnected()
  Module canonical.launchpad.webapp.adapter, line 123, in _ensureConnected
    raise DisconnectionError('Already disconnected')
DisconnectionError: Already disconnected

Perhaps this isn't a mailing list problem, but just manifests itself in the
XMLRPC interface?