Long Time since I used WMP9. I much prefer WMP10 now I`ve got used to the interface. When I had this problem I simply deleted everything in the library and then got the player to search for the music again. In the Library click on the first album, scroll down to the last and hold the shift key whilst you select it. Hit the delete key. If you want to select them individually hold the control key whilst you click them. (This is useful if you`ve not too many duplicates or you`ve entered your own titles and tracks which WMP may not pick up automatically.