seems like your lowpoly is also projecting onto the bake , just select the lowpoly , right click , properties and deselect "cast shadows" that should do it :) nice shottie !
the udn one might be long. It uses "Incl./Excl. Object ID" option in the AO material though which might very well solve the problem. And i dont think somebody mentioned that so far. Yeah this happened to me alot of times before as well. I apply a push modifier with a tiny amount to the lowpoly in this case so nothing gets…