Expected Variable or None (got torch.cuda.FloatTensor) how to solve this problem?

Traceback (most recent call last):
File “crnn/crnn_main.py”, line 244, in
cost = trainBatch(crnn, criterion, optimizer)
File “crnn/crnn_main.py”, line 211, in trainBatch
File “/usr/local/lib/python3.5/dist-packages/torch/autograd/variable.py”, line 167, in backward
torch.autograd.backward(self, gradient, retain_graph, create_graph, retain_variables)
File “/usr/local/lib/python3.5/dist-packages/torch/autograd/init.py”, line 99, in backward
variables, grad_variables, retain_graph)
RuntimeError: expected Variable or None (got torch.cuda.FloatTensor)
Exception ignored in: <bound method DataLoaderIter.del of <torch.utils.data.dataloader.DataLoaderIter object at 0x7fcfb7f5f400>>
Traceback (most recent call last):
File “/usr/local/lib/python3.5/dist-packages/torch/utils/data/dataloader.py”, line 333, in del
File “/usr/local/lib/python3.5/dist-packages/torch/utils/data/dataloader.py”, line 319, in _shutdown_workers
File “/usr/lib/python3.5/multiprocessing/queues.py”, line 345, in get
File “”, line 969, in _find_and_load
File “”, line 954, in _find_and_load_unlocked
File “”, line 887, in _find_spec
TypeError: ‘NoneType’ object is not iterable

I meet the same problem ,have you solved it?