problem with writeNPY(img,'path')

I get error on the last line. I am simply trying to normalize and save the image as .npy
    rgb_norm = NormalizeImage(rgbImage);
    rgb_flip = flip(rgb_norm);
    writeNPY(rgb_flip, nor);

The error is:
Attempt to execute SCRIPT writeNPY as a function:
E:\npy-matlab-master\npy-matlab\writeNPY.m

Error in mat_npy_test (line 40)
    writeNPY(rgb_flip, nor);