I did all that you described above but not only did that not work but when I try to re-install the plug in I get the message that the serial # & license keys have already been used, so I'm stuck with no way to reinstall the plug in.

When you try to re-install the plug-in you get the message that the serial number and license key have been already used?  When you run the installer to install the plug-in, it doesn't ask for the serial number and license key for the plugin.  The only time this is asked for is when you register the plugin on Eventide's website to get the license in the first place.  You can only go through the registration process once, but that also wasn't in the instructions that Tom posted above.