A '401 Error' is usually caused by a browser / internet time out, and will mean that your answers to the exam have not been saved. You will need to take the exam again. We thoroughly apologise for the inconvenience.
Please try again ensuring that you are on a compatible browser (like Firefox or Google Chrome) and that you're using a device with a stable internet connection. Please do not leave your browser window open too long, or refresh your page before taking your exam to ensure your session has not timed out. This should resolve the issue for you.