error message 5002

I'm getting this messge when I try to download a tv episode on my Mac Pro that I've paid for, or when I try to purchase a new episode. I've tried log in/out of iTunes, change creditcard details, change Apple ID.

Mac Pro iTunes shows the episode paid but not downloaded as ready for download, but it doesn't download or the error shows up.

Apple TV shows the episode downloaded but gives and error when trying to play

iPad paid for episode, but it won't download, let me buy it again

Doesn't show up as in progress download or downloaded anywhere, any account, any device