Sounds like something has messed up the InstallShield installer on your system.
Did you use any kind of custom uninstaller tools, or registry cleaners or similar? We recommend against them.
If you haven't rebooted yet, please do that first, as it can be required to unload some components that are already inside other processes.
Here is how to remove the Explorer Replacement settings from the registry if the uninstaller is not working:
If you still have problems with the installer after that, try the suggestions here:
Sometimes the error messages aren't always the same as in the guide but one of the solutions still works, so they're all worth a try.