InstallShield's error messages are garbage, unfortunately. It's one reason we plan to replace it in the longer term.
Have you tried all the things in Problems installing Opus ?
Another thing that sometimes fixes problems is to completely delete the
C:\Program Files\GPSoftware
folder and then run the installer. If you can't delete it, rename it (or the files that can't be deleted inside it), then reboot, then try to delete them again. If you still can't delete it, then something outside of Opus is locking the files (maybe antivirus) or the file permissions on the folder are messed up, which may be what's causing the installer to fail as well.