Just how many mods do you have running to not be able to isolate and track this down? lol

Ok for starts go in and turn off all non-blizzard addons and run the game. If you dont get the spam then start turning on the addons. If you only have a few then do one at a time. If you have a ton of addons then maybe try 2-4 at a time to help keep it narrowed down. Once you get the spam again you should be able to tell which addon is doing it.

Based on the message I would be suspicious of any quest/path recommendation type mods you might have.