@dskhudia  thank you for your suggestion.  
I replaced the ‘cat’ modules with n.quantized.FloatFunctional().cat()
But I run into another error -
TypeError: NumPy conversion for Variable[QuantizedCPUQUInt8Type] is not supported
from the line y[0,:,:,0].cpu().data.numpy()
(line 52 in the link above)
How do I convert this quantized variable to numpy ?  Thanks again for your help.