Well... to be sure, my 80 hunter would be the death of me if those buttons didn't work. In fact, if you watch the movie at
http://www.nuiaddon.com/movies/movie01.html you'll see me using them. So something is up.
Pretty much always when something is not clickable that should be, it means there's an invisible panel floating about. Can you check your list of other addons and see if one of them jumps out at you and suggests it might have had a panel in that area of the screen?
As quick test would be to disabled all of your mods except nUI and see if you can click the buttons then. If not, let me know. Otherwise, you can start re-enabling your mods a few at a time and test each time to see if the problem comes back. If it does, you'll know it was one of the mods you just re-enabled.