Tensorflow error

Traceback (most recent call last):
  File "add_1.py", line 29, in <module>
    scaffold=None, hooks=[saver_hook,summary_hook], chief_only_hooks=None, save_checkpoint_secs=None, save_summaries_steps=True, config=None) as sess:
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/monitored_session.py", line 289, in MonitoredTrainingSession
    return MonitoredSession(session_creator=session_creator, hooks=hooks)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/monitored_session.py", line 447, in __init__
    self._sess = _RecoverableSession(self._coordinated_creator)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/monitored_session.py", line 618, in __init__
    _WrappedSession.__init__(self, self._sess_creator.create_session())
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/monitored_session.py", line 505, in create_session
    self.tf_sess = self._session_creator.create_session()
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/monitored_session.py", line 341, in create_session
    init_fn=self._scaffold.init_fn)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/session_manager.py", line 227, in prepare_session
    config=config)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/session_manager.py", line 173, in _restore_checkpoint
    saver.restore(sess, ckpt.model_checkpoint_path)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/saver.py", line 1388, in restore
    {self.saver_def.filename_tensor_name: save_path})
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/client/session.py", line 766, in run
    run_metadata_ptr)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/client/session.py", line 964, in _run
    feed_dict_string, options, run_metadata)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/client/session.py", line 1014, in _do_run
    target_list, options, run_metadata)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/client/session.py", line 1034, in _do_call
    raise type(e)(node_def, op, message)
tensorflow.python.framework.errors_impl.NotFoundError: Key global_step not found in checkpoint
	 [[Node: save_1/RestoreV2 = RestoreV2[dtypes=[DT_INT32], _device="/job:local/replica:0/task:0/cpu:0"](_recv_save_1/Const_0, save_1/RestoreV2/tensor_names, save_1/RestoreV2/shape_and_slices)]]

Caused by op u'save_1/RestoreV2', defined at:
  File "add_1.py", line 29, in <module>
    scaffold=None, hooks=[saver_hook,summary_hook], chief_only_hooks=None, save_checkpoint_secs=None, save_summaries_steps=True, config=None) as sess:
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/monitored_session.py", line 289, in MonitoredTrainingSession
    return MonitoredSession(session_creator=session_creator, hooks=hooks)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/monitored_session.py", line 447, in __init__
    self._sess = _RecoverableSession(self._coordinated_creator)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/monitored_session.py", line 618, in __init__
    _WrappedSession.__init__(self, self._sess_creator.create_session())
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/monitored_session.py", line 505, in create_session
    self.tf_sess = self._session_creator.create_session()
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/monitored_session.py", line 333, in create_session
    self._scaffold.finalize()
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/monitored_session.py", line 160, in finalize
    lambda: training_saver.Saver(sharded=True, allow_empty=True,
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/monitored_session.py", line 208, in get_or_default
    op = default_constructor()
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/monitored_session.py", line 161, in <lambda>
    write_version=saver_pb2.SaverDef.V2))
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/saver.py", line 1000, in __init__
    self.build()
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/saver.py", line 1030, in build
    restore_sequentially=self._restore_sequentially)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/saver.py", line 620, in build
    restore_sequentially, reshape)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/saver.py", line 404, in _AddShardedRestoreOps
    name="restore_shard"))
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/saver.py", line 361, in _AddRestoreOps
    tensors = self.restore_op(filename_tensor, saveable, preferred_shard)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/training/saver.py", line 200, in restore_op
    [spec.tensor.dtype])[0])
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/ops/gen_io_ops.py", line 441, in restore_v2
    dtypes=dtypes, name=name)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/framework/op_def_library.py", line 759, in apply_op
    op_def=op_def)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/framework/ops.py", line 2240, in create_op
    original_op=self._default_original_op, op_def=op_def)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/framework/ops.py", line 1128, in __init__
    self._traceback = _extract_stack()

NotFoundError (see above for traceback): Key global_step not found in checkpoint
	 [[Node: save_1/RestoreV2 = RestoreV2[dtypes=[DT_INT32], _device="/job:local/replica:0/task:0/cpu:0"](_recv_save_1/Const_0, save_1/RestoreV2/tensor_names, save_1/RestoreV2/shape_and_slices)]]