XT3 Latitude Tablet buttons not allowing me to customize them even with the software installed

As the subject states my computer will not allow me to customize the tablet buttons even with the software installed, even though all of the tablet buttons work when in tablet mode.

More specifically, I'm asking because I would like to change the XT3 Latitude Tablet Back button to be customized for another function. I believe I have the most current dell driver software, that being the feature enhancement pack, but I'm still unsure of the casue. Any response to this post would be very much appreciated.

Thanks