Solved by ptrblck in post #3 
              
              
                The output of your first nn.ConvTranspose2d layer will be [batch_size, 64, 3, 3], which is too small for the next one, which uses a kernel size of 4. 
You could use a kernel size of 4 for the first nn.ConvTranpose2d layer. 
This, however, will yield an error in the last one, since you are using nn.C…