If you are in a country where re-downloading is possible (check this with iTunes in the Cloud and iTunes Match Availability by Country - http://support.apple.com/kb/HT5085), delete the track (and the original file) and download again (Downloading [using iOS or computer] past purchases from the App Store, iBookstore, and iTunes Store - http://support.apple.com/kb/ht2519). See tips on downloading in https://discussions.apple.com/message/19097773, especially unchecking the "Allow Simultaneous Downloads" box in the downloads tab of iTunes.
Select the store on the left side of iTunes.
Click on Purchased on the right side under Quick Links.
You can re-download your available previous purchases.
If you cannot download a second time, contact iTunes Store support staff through the report a problem links in your account history or,
iTunes Customer Service Contact - http://www.apple.com/support/itunes/contact.html > Get iTunes support via Express Lane > iTunes > iTunes Store