Above is from nova-api, but I also noticed compute was tossing the error as well:

2011-06-06 21:58:40,394 ERROR nova [-] Exception during message handling
(nova): TRACE: Traceback (most recent call last):
(nova): TRACE:   File "/usr/lib/pymodules/python2.6/nova/rpc.py", line 232, in _process_data
(nova): TRACE:     rval = node_func(context=ctxt, **node_args)
(nova): TRACE:   File "/usr/lib/pymodules/python2.6/nova/exception.py", line 87, in _wrap
(nova): TRACE:     return f(*args, **kw)
(nova): TRACE:   File "/usr/lib/pymodules/python2.6/nova/compute/manager.py", line 247, in run_instance
(nova): TRACE:     "vpn": is_vpn}})
(nova): TRACE:   File "/usr/lib/pymodules/python2.6/nova/rpc.py", line 540, in call
(nova): TRACE:     rv = list(rv)
(nova): TRACE:   File "/usr/lib/pymodules/python2.6/nova/rpc.py", line 529, in wait
(nova): TRACE:     raise result
(nova): TRACE: RemoteError: IOError Socket closed
(nova): TRACE: ['Traceback (most recent call last):\n', '  File "\\/usr\\/lib\\/pymodules\\/python2.6\\/nova\\/rpc.py", line 239, in _process_data\n    msg_reply(msg_id, rval, None)\n', '  File "\\/usr\\/lib\\/pymodules\\/python2.6\\/nova\\/rpc.py", line 403, in msg_reply\n    publisher = DirectPublisher(connection=conn, msg_id=msg_id)\n', '  File "\\/usr\\/lib\\/pymodules\\/python2.6\\/nova\\/rpc.py", line 386, in __init__\n    super(DirectPublisher, self).__init__(connection=connection)\n', '  File "\\/usr\\/lib\\/pymodules\\/python2.6\\/carrot\\/messaging.py", line 653, in __init__\n    self.declare()\n', '  File "\\/usr\\/lib\\/pymodules\\/python2.6\\/carrot\\/messaging.py", line 664, in declare\n    auto_delete=self.auto_delete)\n', '  File "\\/usr\\/lib\\/pymodules\\/python2.6\\/carrot\\/backends\\/pyamqplib.py", line 240, in exchange_declare\n    return self.channel.exchange_declare(exchange=exchange,\n', '  File "\\/usr\\/lib\\/pymodules\\/python2.6\\/carrot\\/backends\\/pyamqplib.py", line 179, in channel\n    self._channel_ref = weakref.ref(self.connection.get_channel())\n', '  File "\\/usr\\/lib\\/pymodules\\/python2.6\\/carrot\\/connection.py", line 150, in get_channel\n    return self.connection.channel()\n', '  File "\\/usr\\/lib\\/pymodules\\/python2.6\\/carrot\\/connection.py", line 120, in connection\n    self._connection = self._establish_connection()\n', '  File "\\/usr\\/lib\\/pymodules\\/python2.6\\/carrot\\/connection.py", line 133, in _establish_connection\n    return self.create_backend().establish_connection()\n', '  File "\\/usr\\/lib\\/pymodules\\/python2.6\\/carrot\\/backends\\/pyamqplib.py", line 195, in establish_connection\n    connect_timeout=conninfo.connect_timeout)\n', '  File "\\/usr\\/lib\\/pymodules\\/python2.6\\/amqplib\\/client_0_8\\/connection.py", line 140, in __init__\n    (10, 30), # tune\n', '  File "\\/usr\\/lib\\/pymodules\\/python2.6\\/amqplib\\/client_0_8\\/abstract_channel.py", line 89, in wait\n    self.channel_id, allowed_methods)\n', '  File "\\/usr\\/lib\\/pymodules\\/python2.6\\/amqplib\\/client_0_8\\/connection.py", line 198, in _wait_method\n    self.method_reader.read_method()\n', '  File "\\/usr\\/lib\\/pymodules\\/python2.6\\/amqplib\\/client_0_8\\/method_framing.py", line 215, in read_method\n    raise m\n', 'IOError: Socket closed\n']