Eu apenas segui o conselho da Apple dado em esta página , onde eles dizem:
Se você estiver usando o Mac OS X, siga estas etapas:
Quit iTunes. Go to your iTunes Media folder. By default, it's in ~/Music/iTunes. (This folder may be named iTunes Music if you created your iTunes library in iTunes 9 or earlier.) Note: "~" represents your Home folder. Other users on your computer can't access these locations. Drag the iTunes Media folder to a public location. For example, you could move it to the Public folder in your Home folder (~/Public) or to a location outside your Home folder that other users can access (/Users/Shared). Important: Don't move the iTunes folder, the iTunes library file, or the iTunes library.xml file. Open iTunes. Choose iTunes > Preferences. Click Advanced. Click the Change button. In the window that opens, go to your iTunes Media folder. Click Choose or Open.
e perdi cerca de 5 GB porque cada música foi duplicada! Obrigado maçã!