TypeError: ufunc 'add' did not contain a loop with signature matching types dtype('S32') dtype('S32') dtype('S32')

[kocharshaivi19]

Hi,
I am facing issues at this line:

deep-visualization-toolbox/optimize/gradient_optimizer.py

Line 278 in ba520e6

backout = self.net.backward_from_layer(params.push_layer, diffs if is_conv else diffs[:,:,0,0])

and it says:
File "/share/apps/caffe/20170108/intel/python/caffe/pycaffe.py", line 157, in _Net_backward
outputs = set(self.inputs + diffs)
TypeError: ufunc 'add' did not contain a loop with signature matching types dtype('S32') dtype('S32') dtype('S32')

I have tried changing the dtype of diffs to string(S32) and float32, but getting the same error again and again.
Can anyone help resolve this issue by letting me know what can be possible change?

P.S. I am using self.net.backward(diffs=diffs if is_conv else diffs[:,:,0,0]])

Thank you :)