RHUA sync fails with CDS servers with error "pulp.cds.cdslib:ERROR: cdslib:218 Error performing repo sync"

Issue

I have set up an RHUA server following the "Red Hat Update Infrastructure 2.1" PDF, and when I get to the part where the CDS server is added and a sync is initiated, I get an error.

2014-01-30 14:49:50,640 5837:139688297768704: pulp.cds.cdslib:INFO: cdslib:351 CDS sync for repo <{'name': 'Red Hat Update Infrastructure 2 (RPMs) (6Server-x86_64)', 'publish': True, 'relativ
e_path': 'content/dist/rhel/rhui/server/6/6Server/x86_64/rhui/2/os', 'source': {'url': 'https://cdn.redhat.com//content/dist/rhel/rhui/server/6/6Server/x86_64/rhui/2/os', 'type': 'remote'}, '
_id': 'rhel-x86_64-6-rhui-2-rpms-6Server-x86_64', 'arch': 'noarch', 'id': 'rhel-x86_64-6-rhui-2-rpms-6Server-x86_64'}> at

And here is the pulp.log from the RHUA server:

2014-01-30 14:51:19,616 12107:139693486647040: pulp.server.api.cds:INFO: cds:627 CDS sync completed for example.redhat.com at 2014-01-30T14:51:19-05:00
2014-01-30 14:51:19,617 12107:139693486647040: pulp.server.tasking.task:ERROR: task:478 Task failed: Task d2b3d363-89e6-11e3-a65d-005056a1657c: CdsApi.cds_sync(example.rhui.com, )
Traceback (most recent call last):
  File "/usr/lib/python2.6/site-packages/pulp/server/tasking/task.py", line 424, in run
    result = self.callable(*self.args, **self.kwargs)
  File "/usr/lib/python2.6/site-packages/pulp/server/api/cds.py", line 592, in cds_sync
    self.dispatcher.sync(cds, payload)
  File "/usr/lib/python2.6/site-packages/pulp/server/cds/dispatcher.py", line 137, in sync
    self._send(stub.sync, data)
  File "/usr/lib/python2.6/site-packages/pulp/server/cds/dispatcher.py", line 169, in _send
    result = func(*args)
  File "/usr/lib/python2.6/site-packages/gofer/rmi/stub.py", line 72, in __call__
    return self.stub._send(request, opts)
  File "/usr/lib/python2.6/site-packages/gofer/rmi/stub.py", line 133, in _send
    return self.__send(request, options)
  File "/usr/lib/python2.6/site-packages/gofer/rmi/stub.py", line 164, in __send
    any=opts.any)
  File "/usr/lib/python2.6/site-packages/gofer/rmi/policy.py", line 144, in send
    return self.__getreply(sn, reader)
  File "/usr/lib/python2.6/site-packages/gofer/rmi/policy.py", line 181, in __getreply
    return self.__onreply(envelope)
  File "/usr/lib/python2.6/site-packages/gofer/rmi/policy.py", line 197, in __onreply
    raise RemoteException.instance(reply)
PulpException: Error on the CDS during sync; check the server log for more information