This is a change introduced by Adobe, which has altered the default setting for view mode in Adobe Reader 9. In order to access links, users need to change their settings so that the document is not in view mode. In Adobe Reader 9, go to the Edit menu and click Preferences. In the Categories list, click Documents. Under PDF/A View Mode, change the selection from Only for PDF/A documents to Never, and click OK.
Additional details on changing the setting can be located via the Adobe help site: http://help.adobe.com/en_US/Acrobat/9.0/Standard/WS3E0E8467-B787-4020-A1D3-6BC762A42DF2.w.html