About Protected Media Files

From the Windows Media Player Help File:

"Licensed or protected files are digital media files that are secured with a license to prevent illegal distribution. The license can specify whether it expires and how you can use the file. For example, a license can specify whether you can copy the file to a portable device. The terms of the license are specified by the person or company that provided the file. Windows Media Player cannot play protected files without a license."

For more information, including how to obtain such licenses, limits to restoring them, and various rules applying to them:

1. Open Windows Media Player, and go to Help > Help Topics.
2. Expand "Understanding digital media concepts" in the Table of Contents.
3. Read "Understanding licensed files".