Thank you Marco!
I modified my code, as @marco0410 to make to sure the the image size before unflattening matches the image size in the view before activating the first fully connected network:
In my constructor for the class LeNet:
self.fc1 = nn.Linear(4 * kernel_size * kernel_size * 16, 120)  # added 4

In the feed forward network:
x = x.view(-1, 4 * self.kernel_size * self.kernel_size * 16) # added 4