It seems some batchnorm layer in your generator does not use the same number of input channels as the output channels of the preceding conv layer.
E.g.:
...
nn.ConvTranspose2d( ngf * 2, ngf * 16, 4, 2, 1, bias=False),
nn.BatchNorm2d(ngf * 16),
...

Here you can see that the nn.BatchNorm2d takes ngf*16 input channels, which corresponds to the same number of output channels of nn.ConvTranspose2d.
Could you check these numbers?