Wanted to share my resolution to a recent problem. Some review participants with Adobe Reader 9 were unable to connect to the review server (SharePoint), and could not see the Shared Review Information Bar (which displays the options to Check For New Comments or Publish Comments). Other reviewers had no trouble at all.
We confirmed that the server location was properly setup via the wizard in Acrobat Pro 9. The reviewers had correct permissions in SharePoint. They uninstalled and reinstalled the latest version of Reader, downloaded directly from the Adobe site. All to no avail.
What finally made a difference was a change to Internet Explorer settings. The SharePoint site was in our company intranet, but it was not consistently recognized as an intranet site. Therefore it did not automatically rely on the reviewer's Windows authentication settings when joining a PDF review. Adding the root URL of the SharePoint server to the Intranet Zone, and allowing automatic login, cleared up the problem.
Procedure: In Internet Explorer, choose Tools > Internet Options > Security tab > Sites, and add the SharePoint root URL. Return to the Security tab, and choose Custom level. At the bottom of the Settings list, in the User Authentication | Logon section, make sure that "Automatic logon" (e.g., "only in the Intranet zone") is selected.