"Couldn't lower all tuples" when export model with onnx

When i export the onnx model, i got the error:

Traceback (most recent call last):
  File "/home/opluss/Documents/deploy/FSD_deploy/fsd/deploy/onnx.py", line 60, in <module>
    verbose=True
  File "/home/opluss/anaconda3/envs/py37torch17/lib/python3.7/site-packages/torch/onnx/__init__.py", line 230, in export
    custom_opsets, enable_onnx_checker, use_external_data_format)
  File "/home/opluss/anaconda3/envs/py37torch17/lib/python3.7/site-packages/torch/onnx/utils.py", line 91, in export
    use_external_data_format=use_external_data_format)
  File "/home/opluss/anaconda3/envs/py37torch17/lib/python3.7/site-packages/torch/onnx/utils.py", line 639, in _export
    dynamic_axes=dynamic_axes)
  File "/home/opluss/anaconda3/envs/py37torch17/lib/python3.7/site-packages/torch/onnx/utils.py", line 421, in _model_to_graph
    dynamic_axes=dynamic_axes, input_names=input_names)
  File "/home/opluss/anaconda3/envs/py37torch17/lib/python3.7/site-packages/torch/onnx/utils.py", line 159, in _optimize_graph
    torch._C._jit_pass_lower_all_tuples(graph)
RuntimeError: Couldn't lower all tuples.

What does the tuples mean? What are the possible reasons?