try this:
1. Copy ‘iTunes 4 Music Library’ and ‘iTunes Music Library.xml’ out of your Music/iTunes folder. Put them on your Desktop.
2. Delete those two files from your Music/iTunes folder. Now the only
thing in there will be your ‘iTunes Music’ folder (unless you keep that
somewhere else, of course).
3. Start iTunes. It opens up empty. Now quit iTunes. Notice it has
created new, empty ‘iTunes 4 Music Library’ and ‘iTunes Music
Library.xml’ files.
4. Delete those new files. Copy your old files from your Desktop back into your Music/iTunes folder.
 / message  controls
5. Start iTunes again.
(note:i'm not responsible for any messups that mess stuff up)