[Part On!]

Hi All,
I know the answer to this is somewhere in the manual, but, time is growing short before my first gig. When I try to load a new all hits 2000 cdg, it tells me that the book id is already being used, but, I don't believe it is since I only have 7 discs loaded so far. what do you reccomend that I change the new book id to, and how do I do it?
Thanks