初心者です．Githubにアップされているチュートリアル通りにやっています．
https://github.com/Microsoft/CNTK/blob/master/Tutorials/CNTK_205_Artistic_Style_Transfer.ipynb

6セル目を実行すると以下のようなエラーが出力されます．解決方法を教えて頂きたいです．

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-7-5c5a134b2d0e> in <module>()
     42 else:
     43     x0 = content
---> 44 xstar = optimize(loss, x0, inner, outer)
     45 plt.imshow(np.asarray(np.transpose(xstar+SHIFT, (1, 2, 0)), dtype=np.uint8))

<ipython-input-7-5c5a134b2d0e> in optimize(loss, x0, inner, outer)
     30     for i in range(outer):
     31         s = opt.minimize(objfun, img2vec(x0), args=(loss,), method='L-BFGS-B', 
---> 32                          bounds=bounds, options={'maxiter': inner}, jac=True)
     33         print('objective : %s' % s.fun[0])
     34         x0 = vec2img(s.x)

C:\Users\owner\Anaconda3\lib\site-packages\scipy\optimize\_minimize.py in minimize(fun, x0, args, method, jac, hess, hessp, bounds, constraints, tol, callback, options)
    448     elif meth == 'l-bfgs-b':
    449         return _minimize_lbfgsb(fun, x0, args, jac, bounds,
--> 450                                 callback=callback, **options)
    451     elif meth == 'tnc':
    452         return _minimize_tnc(fun, x0, args, jac, bounds, callback=callback,

C:\Users\owner\Anaconda3\lib\site-packages\scipy\optimize\lbfgsb.py in _minimize_lbfgsb(fun, x0, args, jac, bounds, disp, maxcor, ftol, gtol, eps, maxfun, maxiter, iprint, callback, maxls, **unknown_options)
    326             # until the completion of the current minimization iteration.
    327             # Overwrite f and g:
--> 328             f, g = func_and_grad(x)
    329         elif task_str.startswith(b'NEW_X'):
    330             # new iteration

C:\Users\owner\Anaconda3\lib\site-packages\scipy\optimize\lbfgsb.py in func_and_grad(x)
    276     else:
    277         def func_and_grad(x):
--> 278             f = fun(x, *args)
    279             g = jac(x, *args)
    280             return f, g

C:\Users\owner\Anaconda3\lib\site-packages\scipy\optimize\optimize.py in function_wrapper(*wrapper_args)
    290     def function_wrapper(*wrapper_args):
    291         ncalls[0] += 1
--> 292         return function(*(wrapper_args + args))
    293 
    294     return ncalls, function_wrapper

C:\Users\owner\Anaconda3\lib\site-packages\scipy\optimize\optimize.py in __call__(self, x, *args)
     61     def __call__(self, x, *args):
     62         self.x = numpy.asarray(x).copy()
---> 63         fg = self.fun(x, *args)
     64         self.jac = fg[1]
     65         return fg[0]

<ipython-input-7-5c5a134b2d0e> in objfun(x, loss)
     22     v, g = value_and_grads(loss, {loss.arguments[0]: [[y]]})
     23     v = np.reshape(v, (1,))
---> 24     g = img2vec(list(g.values())[0])
     25     return v, g
     26 

<ipython-input-7-5c5a134b2d0e> in img2vec(img)
      6 # utility to convert an image to a vector
      7 def img2vec(img):
----> 8     return img.flatten().astype(np.float64)
      9 
     10 # utility to compute the value and the gradient of f at a particular place defined by binding

AttributeError: 'list' object has no attribute 'flatten'