Comment 4 for bug 1167779

a very similar issue when creating a vlan with nova-manage:

nova-manage --config-file=/etc/nova/nova.conf network create public 10.1.173.0/24 1 256
2013-08-07 16:34:07.655 4948 INFO nova.network.driver [-] Loading network driver 'nova.network.linux_net'
/usr/lib/python2.6/site-packages/nova/openstack/common/db/sqlalchemy/session.py:376: DeprecationWarning: BaseException.message has been deprecated as of Python 2.6
  m = _DUP_KEY_RE_DB[engine_name].match(integrity_error.message)
Command failed, please check log for more info
2013-08-07 16:34:08.019 CRITICAL nova [req-ec84355d-9160-44fa-b302-f2158a681654 None None] Detected existing vlan with id 100
2013-08-07 16:34:08.019 4948 TRACE nova Traceback (most recent call last):
2013-08-07 16:34:08.019 4948 TRACE nova File "/usr/bin/nova-manage", line 1263, in <module>
2013-08-07 16:34:08.019 4948 TRACE nova main()
2013-08-07 16:34:08.019 4948 TRACE nova File "/usr/bin/nova-manage", line 1255, in main
2013-08-07 16:34:08.019 4948 TRACE nova fn(*fn_args, **fn_kwargs)
2013-08-07 16:34:08.019 4948 TRACE nova File "/usr/bin/nova-manage", line 494, in create
2013-08-07 16:34:08.019 4948 TRACE nova net_manager.create_networks(context.get_admin_context(), **kwargs)
2013-08-07 16:34:08.019 4948 TRACE nova File "/usr/lib/python2.6/site-packages/nova/network/manager.py", line 1812, in create_networks
2013-08-07 16:34:08.019 4948 TRACE nova self, context, vpn=True, **kwargs)
2013-08-07 16:34:08.019 4948 TRACE nova File "/usr/lib/python2.6/site-packages/nova/network/manager.py", line 1056, in create_networks
2013-08-07 16:34:08.019 4948 TRACE nova return self._do_create_networks(context, **kwargs)
2013-08-07 16:34:08.019 4948 TRACE nova File "/usr/lib/python2.6/site-packages/nova/network/manager.py", line 1184, in _do_create_networks
2013-08-07 16:34:08.019 4948 TRACE nova network = self.db.network_create_safe(context, net)
2013-08-07 16:34:08.019 4948 TRACE nova File "/usr/lib/python2.6/site-packages/nova/db/api.py", line 804, in network_create_safe
2013-08-07 16:34:08.019 4948 TRACE nova return IMPL.network_create_safe(context, values)
2013-08-07 16:34:08.019 4948 TRACE nova File "/usr/lib/python2.6/site-packages/nova/db/sqlalchemy/api.py", line 96, in wrapper
2013-08-07 16:34:08.019 4948 TRACE nova return f(*args, **kwargs)
2013-08-07 16:34:08.019 4948 TRACE nova File "/usr/lib/python2.6/site-packages/nova/db/sqlalchemy/api.py", line 2165, in network_create_safe
2013-08-07 16:34:08.019 4948 TRACE nova raise exception.DuplicateVlan(vlan=values['vlan'])
2013-08-07 16:34:08.019 4948 TRACE nova DuplicateVlan: Detected existing vlan with id 100
2013-08-07 16:34:08.019 4948 TRACE nova