In function book_made_simple_link it is checked for user_access('create book content'). As this is not an existing user access string, it is only true for user #1. The correct function call should read user_access('add content to books'). I found this in book.module, line 43.
What about a dev version prior to official releases?
Comments
Comment #1
MarcElbichon commentedCorrected in version 2.2 .
Dev versions are located at http://code.google.com/p/mmr-drupal-modules/downloads/list, official releases in Drupal
Comment #2
MarcElbichon commentedComment #3
scottrigby