guymason -
Have seen that before when user's PDF is within a website, and the PDF is referencing a file some where other than the original server.
Netscape --> Advanced --> Settings
or if IE, version 5.0 had documented some of these issues with PDF files. Fix = Install 5.5 sp1
If not browser related, I would have your user download the latest adobe acrobat reader. They've recently released their latest version to incorporate all SVG plugins.
Good luck.