I don't know why you are running into this particular problem, but you may want to look for a different method to do your document reviews. Adobe is retiring the Acrobat Workspaces service, which is used by the shared review when you select to use Acrobat.com. See the FAQ for more information: http://forums.adobe.com/docs/DOC-4203
The next scheduled update for Acrobat will remove this feature.
Karl Heinz Kremer
PDF Acrobatics Without a Net
PDF Software Development, Training and More...
http://www.khkonsulting.com