title: Evaluating payload provided when calling invoke endpoint operation
body: <p>I'm working on a credit fraud dataset on sagemaker. I'm using a linear learner binary classification algorithm. I divided the data into training and test sets and got the results for test set. When I tried to evaluate model performance characteristics on training set, I'm getting the following error</p>
  
  <pre><code> An error occurred (ModelError) when calling the InvokeEndpoint operation: Received client error 
  (400) from model with message "unable to evaluate payload provided".
  </code></pre>
  
  <p>I mentioned the code below</p>
  
  <pre><code>train_data = 's3://{}/{}/{}'.format(bucket, prefix, 'train/examples') #making train_data
  
  #making test_data
  test_key = "{}/test/examples".format(prefix)
  s3.Bucket(bucket).download_file(test_key, 'test_data')
  
  #preparing train channels for training the data
  train_channel = sagemaker.session.s3_input(train_data, content_type='text/csv')
  
  #training the data
  linear.fit(inputs=train_channel,  logs=True)
  
  #creating the endpoint
  linear_predictor = linear.deploy(initial_instance_count=1,
                               instance_type='ml.m4.xlarge')
  
  #getting the results on test_data
  l = []
  with open('test_data', 'r') as f:
  for j in range(0,56962):
      single_test = f.readline()
      result = linear_predictor.predict(single_test)
      l.append(result)
      if j%10000 ==0 :
          print(j)
  print(l[0:10])
  
  #getting the results on train_data
  #THE CODE BELOW IS THROWING THE ABOVE MENTIONED ERROR
  q =[]
  with open('train_data', 'r') as f:
  for j in range(0,56962):
      single_test = f.readline()
      result = linear_predictor.predict(single_test)
      q.append(result)
      if j%10000 ==0 :
          print(j)
  print(q[0:10])
  </code></pre>
  
  <p>I'm getting the results on test data. I stored it in list l. For getting the results on the training set, I followed the similar procedure, but I'm getting the above mentioned error. Can someone please offer a resolution for this?</p>