The real error is:
2012-09-05 11:23:00 ERROR nova.rpc.amqp [req-3e174011-b6cd-40ba-9066-5018df246c3e None None] Exception during message handling
2012-09-05 11:23:00 TRACE nova.rpc.amqp Traceback (most recent call last):
2012-09-05 11:23:00 TRACE nova.rpc.amqp File "/usr/lib/python2.7/dist-packages/nova/rpc/amqp.py", line 253, in _process_data
2012-09-05 11:23:00 TRACE nova.rpc.amqp rval = node_func(context=ctxt, **node_args)
2012-09-05 11:23:00 TRACE nova.rpc.amqp File "/usr/lib/python2.7/dist-packages/nova/network/manager.py", line 257, in wrapped
2012-09-05 11:23:00 TRACE nova.rpc.amqp return func(self, context, *args, **kwargs)
2012-09-05 11:23:00 TRACE nova.rpc.amqp File "/usr/lib/python2.7/dist-packages/nova/network/manager.py", line 949, in get_instance_nw_info
2012-09-05 11:23:00 TRACE nova.rpc.amqp network = self._get_network_by_id(context, vif['network_id'])
2012-09-05 11:23:00 TRACE nova.rpc.amqp File "/usr/lib/python2.7/dist-packages/nova/network/manager.py", line 1722, in _get_network_by_id
2012-09-05 11:23:00 TRACE nova.rpc.amqp network_id)
2012-09-05 11:23:00 TRACE nova.rpc.amqp File "/usr/lib/python2.7/dist-packages/nova/network/manager.py", line 1543, in _get_network_by_id
2012-09-05 11:23:00 TRACE nova.rpc.amqp return self.db.network_get(context, network_id)
2012-09-05 11:23:00 TRACE nova.rpc.amqp File "/usr/lib/python2.7/dist-packages/nova/db/api.py", line 755, in network_get
2012-09-05 11:23:00 TRACE nova.rpc.amqp return IMPL.network_get(context, network_id)
2012-09-05 11:23:00 TRACE nova.rpc.amqp File "/usr/lib/python2.7/dist-packages/nova/db/sqlalchemy/api.py", line 120, in wrapper
2012-09-05 11:23:00 TRACE nova.rpc.amqp return f(*args, **kwargs)
2012-09-05 11:23:00 TRACE nova.rpc.amqp File "/usr/lib/python2.7/dist-packages/nova/db/sqlalchemy/api.py", line 1935, in network_get
2012-09-05 11:23:00 TRACE nova.rpc.amqp raise exception.NetworkNotFound(network_id=network_id)
2012-09-05 11:23:00 TRACE nova.rpc.amqp NetworkNotFound: Network 1 could not be found.