Because of security set up at the client's site, it was necessary to add the web viewer url as a trusted site and this corrected the problem.
From the IE Browser Window, select
- Internet Options
- Click on Trusted Sites
- Click on the Sites Button
- Put the Web Viewer URL in the box labelled Add this website to the zone
- Select Add
- Select Close
If you are NOT using HTTPS, you may need to uncheck 'Enable Protected Mode' and restart the browser.