iTunes is little more than a database with a front-end that lets you view its contents, and play the files it manages. As such, it contains a library file, which stores information about your media files. In some cases, this library file can get corrupted, causing a variety of problems.
Doug Adams, manager of Doug’s AppleScripts for iTunes, published a short AppleScript that can check your iTunes library for corruption. As Doug says:
iTunes can seem to behave normally even if there are tracks with corrupted track entry data or corrupted metadata in their files. So you might not even be aware of corruption until a third-party appliance elicits errors.
Go to Doug’s site, run the AppleScript, and check if there are any errors. As Doug explains:
This will error when it finds some badly encoded or improper UTF-8 text, which is often the culprit. Then it’s just a matter of finding the troublesome tracks in iTunes and fixing the problems if possible. Usually this means just editing the tags in iTunes.