Apparently, Windows, Mac, and Unix all use a different type of carriage return and this is looking for the Unix one. In order to convert your books, you can use Notepad++ and double-click where it says Windows (CR LF) on the bottom right to change it to Unix (LF), or if you're using the basic Notepad, you'll have to open a txt file that's already formatted with the Unix type (check the PlayBook zip file) and paste the contents of your book there.