I had a similar problem before with iphone 4s and downloads that worked on phone but later not on computer.
METHOD 1. Assuming computer has been restarted since then, restart iTunes on computer. Go back to check for available purchases to download. Select download all. If store doesn't recognize that the file is corrupted then delete it see method 2.
METHOD 2. Delete corrupted file from computer. Select the file on your Mac anf press delete key and option key at the same time. Shift plus delete key does the the same thing on Windows computer.
The following dialogue will appear: “Are you sure you want to remove the selected song from your iTunes library?”
Say yes and send it to the trash. You should be able to go back to the store (see method 1 above and download the file).
If that doesn't get it here is some instructions from apple support site:
Note: Downloading of previously purchased movies is available in the United States only.
- Open iTunes 10.6 or later on your computer. (You can download the latest version of iTunes here.)
- If you're not already signed in, click Sign In, and enter your Apple ID and password.
- After you've signed in, click Purchased on the right side in the iTunes Store under the QUICK LINKS section.
- From your Purchased page, click the tab for the content type you're looking for (Music, Movies, TV Shows, Apps, or Books).
- Click Songs or Albums to change the page view and All or "Not in My Library" to view your purchased content that currently is not downloaded on your computer.
- Click the download icon to the right of each item to download that item.
- To download previous purchases on a computer, your computer must be authorized for the Apple ID that was used for the original purchase. For more information about iTunes Store authorization and deauthorization see, this article.
- If they are offered for purchase in 1080p, you can download previously purchased 720p HD TV shows and movies in 1080p. Learn more about downloading in 1080p.
- Previous purchases may be unavailable if they have been refunded or are no longer on the iTunes Store. Downloading previously purchased movies and TV shows requires iTunes 10.6 or later.
Additional InformationLearn more about which content types are supported for iTunes in the Cloud by country, as well as where iTunes Match is available.
- Read more about syncing purchased apps from the App Store in this article.
- For information about enabling Automatic Downloads, see this article.
- For information about associating a device or computer to your Apple ID, see this article.
- For information about troubleshooting apps purchased from the App Store, see this article.
- For information about resuming interrupted downloads, see this article.
- For information about watching previously purchased TV Shows on Apple TV (2nd generation), see this article.
- For information about adding a computer or iOS device to iTunes Match, see this article.
- For information about subscribing to iTunes Match, see this article.
Please let me know if this or something else solved your problem. I was really worried when it happened to me.