RuntimeError: index 1 is out of bounds for dimension 1 with size 1

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Traceback (most recent call last):
File "D:/PyCharm/ssd.pytorch-master/train2.py", line 247, in
train()
File "D:/PyCharm/ssd.pytorch-master/train2.py", line 170, in train
loss_l, loss_c = criterion(out, targets)
File "D:\PyCharm\hellopytorch\venv\lib\site-packages\torch\nn\modules\module.py", line 727, in _call_impl
result = self.forward(*input, **kwargs)
File "D:\PyCharm\ssd.pytorch-master\layers\modules\multibox_loss.py", line 95, in forward
loss_c = log_sum_exp(batch_conf) - batch_conf.gather(1, conf_t.view(-1, 1))
RuntimeError: index 1 is out of bounds for dimension 1 with size 1

how to solve this problem