Xubin, I ran into the same problem. Your method did not work for me. It seems to be an issue with 8.0.0.8 finding the correct version of DVDFabPasskey.exe to associate with when more than one version has been installed in the past. In my case, the reg file was trying to latch onto an old beta 7 version. I got around the issue by going into the directory where Passkey was installed and running RegDVDFabPasskey.exe and then browsing to my reg file. Then it took the registration info properly....:)
Uninstalling the old beta 7 version did not help either, just in case someone is thinking of going that route.