Can't Download Free Lectures

I'm taking an online course. Part of our reading material was Stein's book, A Basic Guide to Interpreting the Bible. Since i missed this whole section of the course, I was told there were audio files i can listen to and catch up. I still bought Stein's book which i haven't received from Amazon yet. I'm wondering why i can't finish downloading his lectures and I'm also wondering what the difference is between the lectures one pays for and those that are free. To be sure, I did read the FAQ stating that the lectures that are paid for have quizzes etc. Is there a list or something compare them to the free ones?

Thanks!