This is unfortunately expected - as of Dec 15th 2009 the old activation server which was used for Acrobat 7 (ACS3) was decommisioned. This server was needed to do any migrations to Digital Editions. It is also worth noting that this was the activation server used to activate Acrobat 7, although this capability was no longer available as of April 2009, so you will not be able to activate Acrobat 7 to read that content on a new machine.
If possible you should contact the place where you purchased the content to see if you can redownload it to get it to view in Digital Editions.
This is totally unacceptable. Adobe has failed to honor the obligation it took on when it created it's DRM scheme. Here we have a textbook case against any form of DRM. Adobe took away my 'rights'.