We ran across this error in Windows XP with Windows Media Player 8.

Error: Windows Media Player cannot play this file. Connect to the Internet or insert the removable media on which the file is located, and then try to play the file again.

Symptoms: Media files (mp3, avi, mpeg) will play on the computer but not stream across the local network (lan) or over the internet.

The fix we found: Hit Start > All Programs > Accessories > System Tools > System Restore.