Apparently, I'm not the only one who is having trouble with iTunes store tracks playing. Sometime, perhaps 2 weeks ago, I noticed certain tracks would not transfer to my iPod, nor would they even play in iTunes. Several tracks were over a year old, and had played many times without problem.
MacFixIt - What to do if iTunes-purchased tracks won't transfer to iPod:
A growing number of MacFixIt readers are reporting an issue where tracks purchased through the iTunes Music Store do not automatically transfer to an iPod during the on-connect synchronization process.
After some back and forth with Apple re: this issue, Apple authorized me to re-download all files. They said:
Having carefully considered your request, we will allow you to re-download the titles that you have purchased from the iTunes Music Store. To download again, open iTunes and select Check for Purchased Music from iTunes' Advanced menu.Please note that this is a one-time exception to the iTunes Music Store Terms of Service. We strongly advise that you back up your hard disk regularly. This will prevent you from having to purchase replacement copies of your songs should they be lost.
Apple never gave me a good reason as to why this error occurred however.
These are a few other (canned) suggestions from Apple, none which even directly applied to my problem:
Having McAfee Privacy Service installed on your computer prevents you from downloading music from the iTunes Music Store. You may download your music using a different computer or temporarily remove McAfee Privacy Service.
The error you have encountered may also be caused by the presence of web acceleration software. Many Internet service providers include this with their setup software and it may prevent connection to the Music Store.
In accordance with the contracts between the iTunes Music Store, the artists, and the record companies, you may authorize five computers to play music purchased using your iTunes Music Store Account.