I replaced the nice raise CertificateError with just a 'raise "blah"' to get a backtrace. This is what I got:

bzr: ERROR: exceptions.TypeError: exceptions must be old-style classes or derived from BaseException, not str

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 920, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 1131, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 673, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.7/dist-packages/bzrlib/commands.py", line 695, in run
    return self._operation.run_simple(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/cleanup.py", line 136, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/cleanup.py", line 166, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/bzrlib/builtins.py", line 1420, in run
    from_location)
  File "/usr/lib/python2.7/dist-packages/bzrlib/controldir.py", line 778, in open_tree_or_branch
    controldir = klass.open(location)
  File "/usr/lib/python2.7/dist-packages/bzrlib/controldir.py", line 685, in open
    t = _mod_transport.get_transport(base, possible_transports)
  File "/usr/lib/python2.7/dist-packages/bzrlib/transport/__init__.py", line 1679, in get_transport
    return get_transport_from_url(location_to_url(base), possible_transports)
  File "/usr/lib/python2.7/dist-packages/bzrlib/transport/__init__.py", line 1601, in location_to_url
    location = directories.dereference(location)
  File "/usr/lib/python2.7/dist-packages/bzrlib/directory_service.py", line 65, in dereference
    return service().look_up(name, url)
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/launchpad/lp_directory.py", line 68, in look_up
    return self._resolve(url)
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/launchpad/lp_directory.py", line 173, in _resolve
    result = self._resolve_via_xmlrpc(path, url, _request_factory)
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/launchpad/lp_directory.py", line 100, in _resolve_via_xmlrpc
    result = resolve.submit(service)
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/launchpad/lp_registration.py", line 271, in submit
    self._authenticated)
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/launchpad/lp_registration.py", line 194, in send_request
    result = method(*method_params)
  File "/usr/lib/python2.7/xmlrpclib.py", line 1224, in __call__
    return self.__send(self.__name, args)
  File "/usr/lib/python2.7/xmlrpclib.py", line 1578, in __request
    verbose=self.__verbose
  File "/usr/lib/python2.7/dist-packages/bzrlib/plugins/launchpad/lp_registration.py", line 72, in request
    response = self._opener.open(request)
  File "/usr/lib/python2.7/urllib2.py", line 400, in open
    response = self._open(req, data)
  File "/usr/lib/python2.7/urllib2.py", line 418, in _open
    '_open', req)
  File "/usr/lib/python2.7/urllib2.py", line 378, in _call_chain
    result = func(*args)
  File "/usr/lib/python2.7/dist-packages/bzrlib/transport/http/_urllib2_wrappers.py", line 926, in https_open
    connection.connect_to_origin()
  File "/usr/lib/python2.7/dist-packages/bzrlib/transport/http/_urllib2_wrappers.py", line 511, in connect_to_origin
    match_hostname(peer_cert, self.host)
  File "/usr/lib/python2.7/dist-packages/bzrlib/transport/http/_urllib2_wrappers.py", line 444, in match_hostname
    raise "blah"
TypeError: exceptions must be old-style classes or derived from BaseException, not str

You can report this problem to Bazaar's developers by running
    apport-bug /var/crash/bzr.1000.2012-03-02T10:54.crash
if a bug-reporting window does not automatically appear.