Yesterday I downloaded and installed the latest and greatest iTunes (version 18.104.22.168). Since then, when I download podcasts, I occasionally receive the error message err = -39. According to Apple, the cause is incompatibility between iTunes and some web acceleration software. Guess what? I’m not using web acceleration software.
Manson2k, over at Red Kawa, suggests it may be due to ReadyBoost on Windows Vista. In my case, I already have ReadyBoost disabled.
Thinking that it is probably just a corrupted cache as the episodes were receiving the -39 error but had downloaded some of the file. When I searched the computer for an episode name, I discovered that there were a few .tmp files in my Z:\\Music\\Downloads directory with the same names of podcast episodes that were receiving the -39 error. Deleting these files allowed iTunes to download the episodes correctly.
Obviously, there seems to be many causes of the -39 error. I hope Apple fixes this bug or at least gives the option to clear the download cache from iTunes.