Hi @ptrblck,
First of all , thanks a lot for your help.
I changed the code as you mentioned and that error is gone. 
However , I am getting error in
---> 90 return F.upsample_bilinear(self.final, x.size()[2:])
in this line
The error is :
AttributeError: 'Sequential' object has no attribute 'dim'
Could you please help ?
Thanks in advance.