Hi,
To resolve this problem, clear the Windows Media Player database. To do this, follow these steps:
- Exit Windows Media Player.
- Click Start, click Run, type %LOCALAPPDATA%\Microsoft\Media Player, and then click OK.
- Select all the files in the folder, and then click Delete on the File menu.
Note: You do not have to delete the folders that are in this folder.
- Restart Windows Media Player.
Note Windows Media Player automatically rebuilds the database.
If this does not resolve the problem, clear the Windows Media Player database cache files. To do this, follow these steps:
- Exit Windows Media Player.
- click Start, click Run, type %LOCALAPPDATA%\Microsoft, and then click OK.
- Select the Media Player folder, and then click Delete on the File menu.
- Restart Windows Media Player.
Note: Windows Media Player automatically rebuilds the database
For more information:
You cannot view, add, or delete items in the library in Windows Media Player 11
http://support.microsoft.com/kb/925718
It is also applicable to windows media player 12.
Also see: http://social.answers.microsoft.com/Forums/en-US/w7music/thread/e68d4e33-897c-421d-8d4b-dbf53c9ee4a5
Thanks and Regards:
Swati Keni- Microsoft Support