I have been working on a book that now has 12 chapters. I had no problem adding the 12 chapters early on. I have since updated from 5.0 to 5.01 about 3 months ago. Now I need to add a TOC but when I try to add a new chapter I get a message that says "This chapter cannot be used in this book because it is stored on a different volume." I tried using different files and creating new files from scratch and saving them but I get the same message whenever I try to add them to the book. Does anyone have any suggestions?