The .plist file is the license file located in User/Library/Preferences/ByHost
I have the Z3TA installed on both my macs, and it looks to me like the problem might have something to do with the OSX version. I have problems on the one running 10.6.8. When I opened the plugin on the machine running 10.7 I got a dialog box asking me to enter the RegCode which is what you need to make it work. That dialog doesn't appear on 10.6.