A few weeks after an intractable -100000 error iTunes error that only resolved when I uses SSH tunneling to download from a California server I ran into a iTunes Store: "Error (-50)" when downloading purchased content with a TV show my son wanted.
I cleared the download cache and deleted the partial download but I was stuck with the problem. I'd already ruled out all the other issues Apple mentions. I certainly didn't use a 'web accelerator' ...
But wait. "Web accelerator" gave me an idea. That suggests a networking issue...
So I used OS X Location switching to swap my CenturyLink DNS services for GoogleDNS (I had both configured). That did it. My download streamed normally.
I wonder if DNS issues with iTunes will get more common; after all, iTunes is a competitor for many DNS providers (though not, I think, CenturyLink).
Perhaps more likely, I wonder if this is related to Apples IPv6 transition.
I'm leaving GoogleDNS running for now.