Hi fnqcairns and welcome,
Not much to go on, but my first guess is that you're using the freeware version...DVDFab HD Decrypter...it has no burn utility. It is a ripper only.
If this is the case, you'll need a burn engine such as Img. It's free and the best there is.
Are you able to view the files when played back from the hdd?
Please post back with the application and version you're using. This will help us to avoid a lot of guesswork.
If you could post a screen shot of the application, it'll help a great deal.