ValueError: Expected target size (2, 256), got torch.Size([2, 256, 256])

Traceback (most recent call last):
File “main_cd.py”, line 83, in
train(args)
File “main_cd.py”, line 15, in train
model.train_models()
File “D:\change detection\change detect\ChangeFormer\models\trainer.py”, line 330, in train_models
self._backward_G()
File “D:\change detection\change detect\ChangeFormer\models\trainer.py”, line 306, in _backward_G
self.G_loss = self._pxl_loss(self.G_pred[-1], gt)
File “D:\change detection\change detect\ChangeFormer\models\losses.py”, line 23, in cross_entropy
ignore_index=ignore_index, reduction=reduction)
File “C:\Users\2021276190015\Anaconda3\envs\BIT-CD\lib\site-packages\torch\nn\functional.py”, line 2422, in cross_entropy
return nll_loss(log_softmax(input, 1), target, weight, None, ignore_index, None, reduction)
File “C:\Users\2021276190015\Anaconda3\envs\BIT-CD\lib\site-packages\torch\nn\functional.py”, line 2228, in nll_loss
out_size, target.size()))
ValueError: Expected target size (2, 256), got torch.Size([2, 256, 256])