Can't download a library book to reader.

I downloaded Adobe Digital Edition to my computer and downloaded a book from the library but I cannot download the book to my Sony reader. I get the following error message when I try to activate the program:

E_AUTH_USERID_INUSE http://adeactivate.adobe.com/adept/AddSignInDirectscrapnsew1@yahoo.com urn:uuid:322eeae4-a006-4b8d-8b81-fea5334311ad

I am using Windows 7 64 bit operating system.

Donna