As I suspected...I'm going to step out on a limb here (if anyone knows more than I, please feel free to step in and correct me)...
With the demise of the HD DVD Format, no mention of the same in any of the updates since Aug. of last year (when it was officially announced that DVDFab would no longer support HD DVD or Blu-Ray, except for the two AACS protections already overcome), and nothing in any of the current releases re HD DVD abilities since Blu-Ray was re-enabled, I have to assume that the authors are not going to offer HD DVD in this product any longer.
It still leaves a rather extensive base of already installed machines and discs without the benefits of the ability to back-up that format with this software, but such is the fate of orphan formats.
That is why I think your HD DVD isn't being acknowledged by DVDFab.
I'm sure an appeal to someone like StormJumper will net you an earlier version of the program that still can handle that format, but don't look for it in future releases of this software.