Purchasing: The “Error -50” message appears when the user attempts to purchase a song or is in the process of downloading a purchased song. The purchase and/or downloads subsequently fail.
Previewing: The previewing issue causes many of the 30-second streaming previews offered in the Music Store to terminate prematurely after anywhere from 3 to 22 seconds. It appears that this issue is independent of the current streaming buffer size and prebuffering options offered in iTunes Preferences.
Though the reasons for the errors are unclear, the issue may have something to do with the recent upgrade to iTunes 4.7.1, which coincided with the release of the iPod shuffle. We invite users to post their experiences/problems in the comments below. Please be sure to include such information as your location and iTunes software version. Click on Read More if you need additional details.
The following are several existing threads on the issue: