I understand that you've been facing difficulty using the 'newff' function, as MATLAB seems to be unable to recognize it. The potential cause of the issue is that MATLAB cannot find a particular built-in function on the search path.
Also, I'd like to clarify that the 'newff' function has been deprecated, and the recommended alternative for creating a feed-forward backpropagation network is the 'feedforwardnet' function.