It is a little known fact that home and office wireless Internet connections must accept interference from such household devices as microwaves, dishwashers, dryers and even other nearby wireless routers. When courses continue to fail to download it is because the wireless signal strength is weak or is experiencing interference.
Rather than try to download the courses wirelessly instead connect to the Internet via an Ethernet cable and try again. If wireless is your only option, move your computer and wireless router closer together to increase the signal received on the computer. You should also avoid running appliances such as the microwave, dishwasher, or dryer. In any event, just keep hitting the Retry button until all courses come through.