I struggled with this for a while on a new Vista 64 system. All the answers are contained here in the forum but I found different pieces in different threads. Here is a consolidated list of corrective actions. Hopefully it will save someone's time:
1. Uninstall DVDFab using the uninstaller.
2. Next, assure a complete Uninstall by following (exactly) the directions provided by StormJumper at http://club.cdfreaks.com/2065659-post1.html and be sure to Reboot.
3. Download latest version from www.dvdfab.com (this is the CSS version, do NOT use non-CSS version from www.dvdfab.net). Install after making sure you have Administrator rights on the user account used to do the Install.
4. Request an updated key from http://www.dvdfab.com/retrieveregkey.htm. Be sure to request a v5.x key, not a 3/4.x key.
5. Save the key attachment that was emailed to you, then double-click it to register the key with DVDFab.
...and thanks to all the contributors that did the real work of figuring out the root issues.