We actually had an issue about the time you downloaded where the various subversions were not in sync, and you could have received an older version by mistake.
As Deckard suggests, you should be fine to overwrite what's in the Interface/Addons/ folder but if that does not work for you, then go ahead and clean it up a bit, then d/l and unzip.
Also note that Auctioneer is all the way on 2823, in the general release part of the Website, so you would do well to update the AuctioneerAdvanced suite as well. See http://auctioneeraddon.com/dl/#preview for the goods.
Hm, I wondering ... perhaps this was caused by the Course.com-Addon-Client ... i installed this a few days ago. From this client I also got problems with auctioneer ... so I guess, my gatherer-issues are caused by this, too.