What textbook? Can you supply a link. I have seen many mathematics ebooks, not one supported by Adobe Digital Editions. I can tell you that many of them are not created properly and have all sorts of errors. This may or may not be the problem with the book you are using. My first recommendation is to contact the company that made the book. They are ultimately responsible for the quality of the book they created.
Worth seeing if the older version is better (it is for most things, though not quite all).
There are lots of bugs in ADE2.0 (and 2.0.1). Try replacing ADE2.0 with the older but more reliable v1.7.2.
(You can have them both installed at once if you like.)
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172