Haha, I reproduce it today.

My way is not to start nova-network, and then run nova boot command.

below is message:
2012-03-28 08:12:22 ERROR nova.compute.manager [req-6274f7dc-4815-4926-b913-b16cba0cc4d6 44c3d88f257a4dc39790c318fcb1a2cc 36cf36c3972a437890e5df7bf9805097] [instance: a26c20ed-72b1-45bc-a7c5-b321824b50b1] Instance failed network setup
(nova.compute.manager): TRACE: Traceback (most recent call last):
(nova.compute.manager): TRACE:   File "/root/test/git/nova/nova/compute/manager.py", line 559, in _allocate_network
(nova.compute.manager): TRACE:     requested_networks=requested_networks)
(nova.compute.manager): TRACE:   File "/root/test/git/nova/nova/network/api.py", line 170, in allocate_for_instance
(nova.compute.manager): TRACE:     'args': args})
(nova.compute.manager): TRACE:   File "/root/test/git/nova/nova/rpc/__init__.py", line 68, in call
(nova.compute.manager): TRACE:     return _get_impl().call(context, topic, msg, timeout)
(nova.compute.manager): TRACE:   File "/root/test/git/nova/nova/rpc/impl_kombu.py", line 674, in call
(nova.compute.manager): TRACE:     return rpc_amqp.call(context, topic, msg, timeout, Connection.pool)
(nova.compute.manager): TRACE:   File "/root/test/git/nova/nova/rpc/amqp.py", line 338, in call
(nova.compute.manager): TRACE:     rv = list(rv)
(nova.compute.manager): TRACE:   File "/root/test/git/nova/nova/rpc/amqp.py", line 299, in __iter__
(nova.compute.manager): TRACE:     self._iterator.next()
(nova.compute.manager): TRACE:   File "/root/test/git/nova/nova/rpc/impl_kombu.py", line 572, in iterconsume
(nova.compute.manager): TRACE:     yield self.ensure(_error_callback, _consume)
(nova.compute.manager): TRACE:   File "/root/test/git/nova/nova/rpc/impl_kombu.py", line 503, in ensure
(nova.compute.manager): TRACE:     error_callback(e)
(nova.compute.manager): TRACE:   File "/root/test/git/nova/nova/rpc/impl_kombu.py", line 553, in _error_callback
(nova.compute.manager): TRACE:     raise rpc_common.Timeout()
(nova.compute.manager): TRACE: Timeout: Timeout while waiting on RPC response.
(nova.compute.manager): TRACE: 
2012-03-28 08:12:22 ERROR nova.rpc.amqp [req-6274f7dc-4815-4926-b913-b16cba0cc4d6 44c3d88f257a4dc39790c318fcb1a2cc 36cf36c3972a437890e5df7bf9805097] Exception during message handling
(nova.rpc.amqp): TRACE: Traceback (most recent call last):
(nova.rpc.amqp): TRACE:   File "/root/test/git/nova/nova/rpc/amqp.py", line 252, in _process_data
(nova.rpc.amqp): TRACE:     rval = node_func(context=ctxt, **node_args)
(nova.rpc.amqp): TRACE:   File "/root/test/git/nova/nova/exception.py", line 138, in wrapped
(nova.rpc.amqp): TRACE:     payload)
(nova.rpc.amqp): TRACE:   File "/root/test/git/nova/nova/notifier/api.py", line 118, in notify
(nova.rpc.amqp): TRACE:     payload = utils.to_primitive(payload, convert_instances=True)
(nova.rpc.amqp): TRACE:   File "/root/test/git/nova/nova/utils.py", line 798, in to_primitive
(nova.rpc.amqp): TRACE:     level=level)
(nova.rpc.amqp): TRACE:   File "/root/test/git/nova/nova/utils.py", line 792, in to_primitive
(nova.rpc.amqp): TRACE:     level=level))
(nova.rpc.amqp): TRACE:   File "/root/test/git/nova/nova/utils.py", line 813, in to_primitive
(nova.rpc.amqp): TRACE:     level=level + 1)
(nova.rpc.amqp): TRACE:   File "/root/test/git/nova/nova/utils.py", line 798, in to_primitive
(nova.rpc.amqp): TRACE:     level=level)
(nova.rpc.amqp): TRACE:   File "/root/test/git/nova/nova/utils.py", line 813, in to_primitive
(nova.rpc.amqp): TRACE:     level=level + 1)
(nova.rpc.amqp): TRACE:   File "/root/test/git/nova/nova/utils.py", line 798, in to_primitive
(nova.rpc.amqp): TRACE:     level=level)
(nova.rpc.amqp): TRACE:   File "/root/test/git/nova/nova/utils.py", line 819, in to_primitive
(nova.rpc.amqp): TRACE:     return unicode(value)
(nova.rpc.amqp): TRACE:   File "/usr/lib/python2.6/site-packages/eventlet/tpool.py", line 219, in __str__
(nova.rpc.amqp): TRACE:     return self._obj.__str__()
(nova.rpc.amqp): TRACE: AttributeError: virConnect instance has no attribute '__str__'
(nova.rpc.amqp): TRACE: