With the new Rev A firmware version v1.15 B04 (2016-08), one must add a "--referer" for this to work, e.g.:
curl -u userid:password http://your_camera_ip/setSystemStream --referer http://your_camera_ip/image.htm -d "ReplySuccessPage=image.htm&ReplyErrorPage=errrimg.htm&BrightnessControl=60&ContrastControl=95&ConfigSystemStream=Save" >/dev/null 2>&1