Blue Harvest - S6-E1
Other mistake: In the scene where the Millennium Falcon has just left the death star after Obi-Wan has been killed, there are two shots of the ship flying away through space. In the second shot, the cockpit is missing. (00:33:35)
Other mistake: Joe Swanson is colored incorrectly. His color scheme is apparently the same as Peter Griffin's when looking at his skin color and hair. It is fixed shortly afterwards. (00:11:54)