An important audio codec is missing from 64bit versions of Windows Vista and Windows 7. Some media files generate an error when using Windows Media Player. Third party media players seem to be affected as well, since some will play the video portion with no audio, and others won’t play the media file at all. This problem even occurs with media files downloaded from Microsoft. The Windows Media Player specific error is: “Windows Media Player cannot play, burn, rip, or sync the file because a required audio codec is not installed on your computer.”
Clicking on the “Web Help” leads you to the following page which isn’t much help: http://www.microsoft.com/windows/windowsmedia/player/webhelp/default.aspx?&mpver=12.0.7600.16385&id=C00D11C7&contextid=68&originalid=C00D0BC2 .
The codec is no longer available from the referenced URL. Search for “ACELP.net Codec by VoiceAge” using your favorite search engine to try to locate it.