nova-list
+--------------------------------------+-------+--------+------------+-------------+--------------------------------------------------------+
| ID                                   | Name  | Status | Task State | Power State | Networks                                               |
+--------------------------------------+-------+--------+------------+-------------+--------------------------------------------------------+
| f2e41617-5300-47ac-af42-a70f4c75b372 | vm168 | ERROR  | -          | Running     | private=10.0.0.4, fdb5:b83e:549a:0:f816:3eff:fec1:14ce |
| 35857d28-09eb-4dd6-9e34-78306ae289c6 | vm173 | ACTIVE | -          | Running     | private=10.0.0.5, fdb5:b83e:549a:0:f816:3eff:fe2d:2d6b |
+--------------------------------------+-------+--------+------------+-------------+--------------------------------------------------------+

nova-compute log

2016-03-15 19:32:59.285 31939 DEBUG nova.compute.resource_tracker [req-20b784fe-ec9c-4a29-9fea-14a777f859c6 - -] Migration instance not found: Instance b9929ce7-90cd-469e-95ca-de36a5822667 could not be found.
Traceback (most recent call last):

  File "/opt/stack/nova/nova/conductor/manager.py", line 85, in _object_dispatch
    return getattr(target, method)(*args, **kwargs)

  File "/usr/local/lib/python2.7/dist-packages/oslo_versionedobjects/base.py", line 181, in wrapper
    result = fn(cls, context, *args, **kwargs)

  File "/opt/stack/nova/nova/objects/instance.py", line 399, in get_by_uuid
    use_slave=use_slave)

  File "/opt/stack/nova/nova/db/sqlalchemy/api.py", line 285, in wrapper
    return f(*args, **kwargs)

  File "/opt/stack/nova/nova/objects/instance.py", line 391, in _db_instance_get_by_uuid
    columns_to_join=columns_to_join)

  File "/opt/stack/nova/nova/db/api.py", line 696, in instance_get_by_uuid
    return IMPL.instance_get_by_uuid(context, uuid, columns_to_join)

  File "/opt/stack/nova/nova/db/sqlalchemy/api.py", line 229, in wrapper
    return f(*args, **kwargs)

  File "/opt/stack/nova/nova/db/sqlalchemy/api.py", line 330, in wrapped
    return f(context, *args, **kwargs)

  File "/opt/stack/nova/nova/db/sqlalchemy/api.py", line 1964, in instance_get_by_uuid
    columns_to_join=columns_to_join)

  File "/opt/stack/nova/nova/db/sqlalchemy/api.py", line 1973, in _instance_get_by_uuid
    raise exception.InstanceNotFound(instance_id=uuid)

InstanceNotFound: Instance b9929ce7-90cd-469e-95ca-de36a5822667 could not be found.