Same issue - reposting this from the (now) multiple reports of this issue over the past 24 hours!
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It's looking like the problem is pretty widespread. I can't get Pirates of the Carribbean: Stranger Tides to download to either my desktop or iPad. On the desktop, it doesn't get past 10MB, starts over and then issues an error - either -50 or 8008. On the iPad, it downloads completely and then restarts the download and never shows up in my purchased content (and will continue to re-download infinitely it seems unless I pause it - but it still shows up there waiting to be re-downloaded. For what it's worth, I'm able to download music and apps without issue and just last week downloaded Cars 2 using the same computers/settings/internet connection.
I tried all the tricks - On the desktop... clearing the iTunes cache/history, removing the tmp movies files in downloads folders, restarting desktop, signing in/out of iTunes store, etc. etc. On the iPad... reset the iPad, signed in/out of iTunes store, downloaded movie trailer, etc. etc. Nothing works.
So, my guess is that their movie/video servers are likely overwhelmed right now. I contacted customer support and all they did was issue me a refund.