Solved by Vrushank98 in post #2 
              
              
                The input that you have passed to summary is a 4D tensor of size ([batch_size, 100, 64, 64]), so before passing that directly to the linear layer, you have to reshape to a 2D Tensor. just add: 
 x = x.view(-1, 100)	//100 = input_channels to the Linear layer 
before x = self.linear(x) in the forward(…