What is nUI-14? That's not how it is distributed and that will no work as intended.
You need to download the nUI+ 5.07.06 (Development) version from here at WoW Interface. You cannot use the version that is currently on Curse.com -- to do that you need to be subscribed to the (free) nUI newsletter at
http://www.nUIaddon.com/plus.html -- once you're subscribed to that, you'll be sent directions on how to access the nUI+ private download area (also free).
Once you have access to the download area, download the current "nUI+ (Development)" version whatever that may be when you get to it, then follow these directions...
- Exit WoW
- go to the [ World of Warcraft ] folder
- rename [WTF] to [WTF.saved] and [Interface] to [Interface.saved]
- log in to WoW, but do not enter the world
- do you have an "AddOns" button at the character selection screen?
- if you do, go back to step 1, you're in the wrong [World of Warcraft] folder
- if you do not, enter the world on any toon
- exit WoW again
- unzip the entire contents of the nUI download ZIP into the [World of Warcraft > Interface > AddOns] folder
- log in to WoW again, but do not enter the world
- if you do not have an "AddOns" button, go back to step 8, you installed nUI incorrectly
- if you do have an addons button, enter the world... everything *should* work now