error delete host on lun

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/djextdirect/provider.py", line 256, in process_normal_request
    result = func( request, *data )
  File "/usr/share/openattic/rpcd/extdirect.py", line 116, in wrapper
    return getattr(hh, func.__name__)(*args, **kwargs)
  File "/usr/share/openattic/rpcd/handlers.py", line 675, in remove
    return self._call_singlepeer_method("remove", id)
  File "/usr/share/openattic/rpcd/handlers.py", line 525, in _call_singlepeer_method
    res = meth(id, *args)
  File "/usr/share/openattic/rpcd/handlers.py", line 313, in remove
    return self._get_model_manager().get(id=id).delete()
  File "/usr/lib/python2.7/dist-packages/django/db/models/base.py", line 695, in delete
    collector.delete()
  File "/usr/lib/python2.7/dist-packages/django/db/models/deletion.py", line 255, in delete
    sender=model, instance=obj, using=self.using
  File "/usr/lib/python2.7/dist-packages/django/dispatch/dispatcher.py", line 185, in send
    response = receiver(signal=self, sender=sender, **named)
  File "/usr/share/openattic/lio/models.py", line 618, in __hostacl_pre_delete
    ProtocolHandler.uninstall_hostacl(instance)
  File "/usr/share/openattic/lio/models.py", line 424, in uninstall_hostacl
    handler.delete(lunctx)
  File "/usr/share/openattic/lio/models.py", line 501, in delete
    self.delete_mapped_luns(lunctx)
  File "/usr/share/openattic/lio/models.py", line 509, in delete_mapped_luns
    lunctx["acl"].mapped_luns.remove(lunctx["mapped_lun"])
  File "/usr/lib/python2.7/dist-packages/django/db/models/fields/related.py", line 589, in remove
    self._remove_items(self.source_field_name, self.target_field_name, *objs)
  File "/usr/lib/python2.7/dist-packages/django/db/models/fields/related.py", line 702, in _remove_items
    model=self.model, pk_set=old_ids, using=db)
  File "/usr/lib/python2.7/dist-packages/django/dispatch/dispatcher.py", line 1