I use the iTunes > Preferences > Advanced library location setting
If you read it carefully I don't think it says that. It says media location which is not the same as your library. Your library has two main components. One is the library file (library.itl) which generates what you see when you open iTunes and is a database file of the media you have and where the files are located. The other is the media files themselves. In changing that setting you simply told iTunes to start storing the media in another location. In moving you might easily have just transferred media but left behind all the other files which are really make up the library as you normally see it.
iTunes: How to move [or copy] your music to a new computer [or another drive] - http://support.apple.com/kb/HT4527
Quick answer if you use iTunes' default preferences settings: Copy the entire iTunes folder (and in doing so all its sub-folders and files) intact to the other drive. Open iTunes and immediately hold down the Option key (shift on Windows), then guide it to the new location of the library.
What are the iTunes library files? - http://support.apple.com/kb/HT1660
More on iTunes library files and what they do - http://en.wikipedia.org/wiki/ITunes#Media_management
What are all those iTunes files? - http://www.macworld.com/article/139974/2009/04/itunes_files.html