Unable to download an ebook to my home PC

I am currently taking a course with the National Institute of Government Purchasing (nigp).  the ebook I am trying to access and download is "Legal Aspects of Public Procurement". I have downloaded Adobe Editions already.  I have followed the e-mail instructions from nigp on how to download the book but it does not work. I keep getting the following error message "A DEPT_NO_TOKEN"; I have an Adobe ID, I have authorized this computer, and used the e-mail.  This has been a frustrating experience.