Moving this discussion to the Adobe Digital Editions forum.
The activation server was brought down for maintenance at January 11, 2013 at 11 P.M. PST. Are you still experiencing this error message?
Version 1.7.2 is the answer to many problems with ADE 2.0.
ADE2.0 regularly seems to have problems with Sony and Nook devices (and some others too?).
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