Did you change something with custom menus? If you are using custom menus, you need to make sure the PDF options are enabled.
I work at this client using remote access to a computer they have set up for me. It seems they have switched from using Acrobat to Nuance, PDF Converter. Everything is working as expected on other machines which still have Adobe Reader installed. So it looks like maybe that when Nuance was installed some part of the web browser plug in was disabled.
Anyone used Nuance instead of Acrobat to provide the web browser plug in needed for PDFs and interactive containers?