Error (-50) when trying to download rented movie?

I am trying to download a movie that I have rented (it's about 80% downloaded so far) but then it stopped. When I click on it again to refresh the downloading, I get "There was a problem downloading (Movie Title). An Unknown error occurred (-50). Please check that the connection to the network is active and try again."

The other day I rented a movie on the same network and it was fine. I'm not sure what this means or how to fix it.

Thanks.