This issue usually only occurs on systems running Windows 95/98 or NT. If you happen to see this error message on Windows XP please check to see if you are running 'Cisco Security Agent' and disable this service before proceeding.
On Windows XP this can also be caused by a version conflict with another version of sensapi.dll that is already installed on the machine. The version on the program CD is version 6.0. If you have a newer version of this file you may see the error message "%1 Is not a valid Win32 application." Rename the existing version of sensapi.dll to sensapi.old and then copy the one from the cdrom into C:\Windows\System32. You can then install without error.