Tensorflow: RuntimeError: Attempted to use a closed Session.

Hello every one, I am getting a stack error while testing new unique data to the model I have trained. The error says " RuntimeError: Attempted to use a closed Session.". I am not much expert with tensorflow. Some may help me to figure out why?. Thanks! @alextp @MicaelCarvalho @jfsantos

print ("Now, Testing the unlabel data and writing the results")
YPredByNNForUnlabeledData = sess.run(tf.argmax(yPredbyNN,1),feed_dict={X: testing_features})
print (YPredByNNForUnlabeledData)
for i in xrange (len(YPredByNNForUnlabeledData)):

if YPredByNNForUnlabeledData[i] == 0:
    ClassLabelFinal.append('classical')

else:
    ClassLabelFinal.append('blues')

cwd = os.getcwd()
Test_dataset_path = ("/Users/MA/Desktop/BluesTest")%cwd
Test_dataset, Total_Instances = load_instances(Test_dataset_path)

timestamps = load_timestamps(Test_dataset)

write_results(timestamps, ClassLabelFinal, 'Result.csv')

Now, Testing the unlabel data and writing the results

RuntimeError Traceback (most recent call last)
in ()
1 print ("Now, Testing the unlabel data and writing the results")
----> 2 YPredByNNForUnlabeledData = sess.run(tf.argmax(yPredbyNN,1),feed_dict={X: testing_features})
3 print (YPredByNNForUnlabeledData)
4 for i in xrange (len(YPredByNNForUnlabeledData)):
5

C:\Users\MA\Anaconda3\lib\site-packages\tensorflow\python\client\session.py in run(self, fetches, feed_dict, options, run_metadata)
764 try:
765 result = self._run(None, fetches, feed_dict, options_ptr,
--> 766 run_metadata_ptr)
767 if run_metadata:
768 proto_data = tf_session.TF_GetBuffer(run_metadata_ptr)

C:\Users\MA\Anaconda3\lib\site-packages\tensorflow\python\client\session.py in _run(self, handle, fetches, feed_dict, options, run_metadata)
900 # Check session.
901 if self._closed:
--> 902 raise RuntimeError('Attempted to use a closed Session.')
903 if self.graph.version == 0:
904 raise RuntimeError('The Session graph is empty. Add operations to the '

RuntimeError: Attempted to use a closed Session.