Aperture 3.4.x: "Open iTunes" button may not work
The "Open iTunes" button may not work in the Music Browser. This can happen when adding DRM-protected music to a slideshow on OS X Lion and OS X Mountain Lion.
This is a known issue. To work around the issue, open iTunes directly and authorize the computer to play DRM-protected songs purchased with your Apple ID. You can then return to Aperture and select the song to use in your slideshow.
For information on how to authorize a computer to play DRM-protected content, see iTunes Store: About authorization and deauthorization.