I get this every single time on first log in of a character. A /reloadui almost always fixes it. I am not sure if it's related to the Nameplates, but when it happens, my nameplates addon loads, no error, but I don't actually see nameplates until I target something and/or zone. Just wanted to mention that as they may be related (since both happen at the same time, every time).

...aming\NCSOFT\WildStar\Addons\CandyBars\CandyBars.lua:532: attempt to index field 'tActionBarsHorz' (a nil value)
stack trace:
...aming\NCSOFT\WildStar\Addons\CandyBars\CandyBars.lua:532: in function <...aming\NCSOFT\WildStar\Addons\CandyBars\CandyBars.lua:531>