Can't disable "Press the Option key five times to turn Mouse Keys on and off"

Apple lets users who occasionally want the use of Mouse Keys to enable/disable it by pressing Option (⌥) five times. I use Maya, so I'm constantly using the Option key to manipulate the camera, and this usage often triggers Mouse Keys. Unfortunately, this disables the rest of my keyboard (see this Apple KB page ) and I can't use other helpful shortcuts. I can of course disable it again, but it's annoying when I have to do it again and again. I went to the appropriate place in System Preferences to disable this (Universal Access > Mouse & Trackpad), but it's greyed out. I've done extensive searching and haven't found anyone with a similar problem. Why is this happening, and how can I stop it?