My network like this:
class MultiDigitsNet(torch.nn.Module):
    def __init__(self):    
        super(MultiDigitsNet, self).__init__()
        self.conv1 = torch.nn.Conv2d(in_channels=3, out_channels=48, kernel_size=5, stride=1, padding=2)
        self.max_pool1 = torch.nn.MaxPool2d(kernel_size=2, stride=2)
        self.relu = torch.nn.ReLU()
    def forward(self, x):
        x = self.max_pool1(self.relu(self.conv1(x)))

When training network, I encountered the following error :

2017-06-29 18-05-33.png1283×498 94.3 KB

I have no idea about the meaning of this error. Why this error is happening and how to deal with it?