This bug popped up when I entered Taelloch in The Ringing Deeps:

x [ADDON_ACTION_BLOCKED] AddOn 'CandyBuckets' tried to call the protected function 'Frame:SetPassThroughButtons()'.
[string "@!BugGrabber/BugGrabber.lua"]:485: in function <!BugGrabber/BugGrabber.lua:485>
[string "=[C]"]: in function `SetPassThroughButtons'

I got the same error while in Hallowfall. I had just completed a world quest and was getting the loot from the quest when the error popped up.

In the chat, I also saw:
"Interface action failed because of an AddOn"