This is common problem in older Single Sign-On product, this problem is not limited to SPS or Unix platform alone.
Older release Single Sign-On product, often generate ".com.zerog.registry.xml" file hidden on disk.
Even after running previouse version uninstaller, the file will still be left there on disk.
In Unix, this file will be under /var directory.
After removing ".com.zerog.registry.xml" file hidden on disk, the installer should be running correctly.
Also, it might be useful to turn on debugging for the installer itself by running the unix command:
then trying the installation process again. This will log additional information to the files in /install-config-info to help with troubleshooting the issue.