Problem while trying to export iTunes library to an xml file (on OS X 10.8, iTunes 11.1.3)
I've managed to solve the main reason I was asking this question... (Although I couldn't make Export Library work from iTunes on my Mountain Lion partition)

I booted into Mavericks and then I copied the iTunes folder from Mountain Lion partition to the Mavericks one and it worked as expected... :-)

My library is migrated, including play counts, playlists, album arts, ratings... Well, it's all there.

Note: The iTunes is up to date on both partitions (version 11.1.3).

Note 2: In order to migrate my iOS devices' backups, I also copied from Mountain Lion to Mavericks the folder ~/Library/Application Support/MobileSync.

I'm still curious why export library was not working, but my problem is gone.