Hi,
First question is are you running the latest 2.02 firmware? If not use it. Second question is was the 3TB drive raw or pre-formated in windows before you installed it. If it was, try putting it back in a windows machine and use disk manager to delete the volume and then reinstall it in the 320. That is assuming you don't have a ton of data on there already. That is about all I can think of right now. Good luck.