This occurs if you are not logged on as a Windows Administrator during installation time. The installation program needs to write to the Windows registry. You need to be logged as a Windows Adminstrator to install the viewer software.
If you are logged on as a Windows Administrator then:
- close down all other applications on your computer before attempting to register again (including firewall and anti-spyware/virus applications);
- make sure Windows is up to date with all relevant patches, drivers, and service packs;
- un-install and then re-install the Viewer application.