In the latest Macintosh operating system "Mavericks," 32-bit support has been dropped from iTunes. This means that certain filetypes will not play in iTunes on a Mac that is updated to Mavericks. If you encounter this issue, you can try using iTunes on an iPhone or iPad (which haven't yet dropped this support). A number of courses are available on our apps as well (see download links below).
We are working hard to resolve this issue quickly. If you have any questions, email firstname.lastname@example.org.