As we have seen over the many years, having Scratch Live read the itunes library is not a rock solid solution. None of us in Rane tech support would recommend it and we all try to steer people from it. This is one of many reasons. Mainly the problems have been the two libraries not matching up and also the library not showing up at all. That can be a nightmare for dj's. This usually occurs each time itunes updates its software.
What we recommend is that you manually import the music into Scratch Live using the 'Files' tab on the main page. It is still o.k. and common for people to use itunes to rip cds and create the needed song files that will wind up going into the Scratch Live library. Ideally you would organize you music files in your own folders. I have a hip hop folder, a rock folder, a reggae folder ect. Once the music is organized on my HD it is very easy for me to open Scratch Live, make a new crate called hip hop, rock, reggae and drag those songs from the folders into it.
This way the music is already organized. You can do all of your tagging changes directly in Scratch Live. We recommend using the crates and smart crates in the software in the same fashion you have been using your playlists and smart playlists inside of itunes. Also in the case of you get to a gig and open the program, but you don't see any crates (currently you have no playlists) its not a show stopper. Simply make a new crate, open the Files tab, drag the folder back into the program and you are ready to gig again in only a few minutes. It's in instances like these that the itunes library stops showing that can take hours to repair.
Here is an easy way to keep everything up to date in your library. If you have a hip hop folder with 1,000 songs make a new crate and call it hip hop. Drag the hip hop folder into the new hip hop crate, simple. Now if you add 100 new songs to the hip hop folder, open the files tab and drag that hip hop folder back onto the original hip hop crate. By dragging the same folder to the same crate, it will only update the crate with the new additions instead of doubling the music. If you dragged that hip hop folder onto your rock crate though, it would add all 1,100 files
In the past we have had people try rebuilding the itunes library but lately we have seen odd characters in the itunes id3 tags causing problems reading that library. There was a tag checker we found on the apple website. Give this a look over and hopefully this can help remedy the issue. Ultimately though, I would start to consider not using Scratch Live to read the itunes library.
Link to apple discussion - discussions.apple.com
Link to suggested solution - mac.softpedia.com
Hopefully this will be helpful.