Happens in every zone, I have toons logged out all over Azeroth.
Through much trial and error I found it appears to be a conflict with the "Swatter" addon included in the "Auctioneer" suite. If I disable "Swatter" the error does not appear. Swatter is an addon that's designed to catch and "swat" bugs (well not swat the bugs itself, but give addon developers the information necessary to do so)
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