Comment 2 for bug 835242

It appears it may be related to the IPs not always getting assigned to the instance. In doing some clean up, I found additional tracebacks in the network manager which could be related, although they are at different times:

2011-08-30 18:21:53,553 ERROR nova.rpc [-] ['Traceback (most recent call last):\n', ' File "/usr/lib/pymodules/python2.6/nova/rpc/amqp.py", line 230, in _process_data\n rval = node_func(context=ctxt, **node_args)\n', ' File "/usr/lib/pymodules/python2.6/nova/network/manager.py", line 531, in get_instance_nw_info\n \'bridge\': network[\'bridge\'],\n', "TypeError: 'NoneType' object is unsubscriptable\n"]
2011-08-30 18:22:07,700 ERROR nova [-] Exception during message handling
(nova): TRACE: Traceback (most recent call last):
(nova): TRACE: File "/usr/lib/pymodules/python2.6/nova/rpc/amqp.py", line 230, in _process_data
(nova): TRACE: rval = node_func(context=ctxt, **node_args)
(nova): TRACE: File "/usr/lib/pymodules/python2.6/nova/network/manager.py", line 514, in get_instance_nw_info
(nova): TRACE: fixed_ip['network_id'] == network['id']]
(nova): TRACE: TypeError: 'NoneType' object is unsubscriptable
(nova): TRACE:

If an instance doesn't receive IPs for some reason, you can't delete the instances since the request fails in the network manager.