I am on MacOS Sierra with CPU only nightly.
tf.git_version is 0.12.0-rc0-1156-g8c18a00-dirty.

The error comes from the gradient calculation in concat_v2 when axis = -1 is used to get the last dimension. I could not find axis=-1 documentation for concat_v2 but that is how crelu is implemented.

Concat_v2 along last dimension as a positive int works fine. The forward pass with axis = -1 also works fine, it is just getting a gradient that gives an error.

Reproduce with:

import tensorflow as tf

inputs = tf.random_normal([64, 32,32, 3])
inputs2 = tf.random_normal([64, 32,32, 3])
hidden = tf.concat_v2([inputs, inputs2], axis=-1)  # axis = 3 works fine
grad = tf.gradients(hidden, [inputs])

with tf.Session() as sess:
print( sess.run(grad))

Gives error:

...which was originally created as op u'concat_v2', defined at:
File "crelu.py", line 5, in
hidden = tf.concat_v2([inputs, inputs2], axis=-1)
File "/Users/mikowals/projects/tensorflow/lib/python2.7/site-packages/tensorflow/python/ops/array_ops.py", line 1062, in concat_v2
name=name)
File "/Users/mikowals/projects/tensorflow/lib/python2.7/site-packages/tensorflow/python/ops/gen_array_ops.py", line 498, in _concat_v2
name=name)
File "/Users/mikowals/projects/tensorflow/lib/python2.7/site-packages/tensorflow/python/framework/op_def_library.py", line 763, in apply_op
op_def=op_def)
File "/Users/mikowals/projects/tensorflow/lib/python2.7/site-packages/tensorflow/python/framework/ops.py", line 2389, in create_op
original_op=self._default_original_op, op_def=op_def)
File "/Users/mikowals/projects/tensorflow/lib/python2.7/site-packages/tensorflow/python/framework/ops.py", line 1264, in init
self._traceback = _extract_stack()

InvalidArgumentError (see above for traceback): Concat dim is out of range: -1 vs. 4
[[Node: gradients/concat_v2_grad/ConcatOffset = ConcatOffset[N=2, _device="/job:localhost/replica:0/task:0/cpu:0"](concat_v2/axis, gradients/concat_v2_grad/Shape, gradients/concat_v2_grad/Shape_1)]]