There will be folks more knowledgeable than me to give you a definite answer, but I'm going to say that it was struck with a broken die. Odd, though, that the break is so clean and matches exactly the curve of edge of the coin.
These guys would know whether or not it's an error: http://conecaonline.org. They had a forum where you could post these pictures, but I see it says it's temporarily down. Let me see if I can get one of them over to this thread.
All I do is crack slabs... but I'd guess it would be worth any good TPG's fee to have it graded/attributed and then go from there.