The TGD looks corrupt, no node network present. As Kadri said, there are no valid groups, so there is no content in any groups, and there are no nodes of any kind in the node network.
Did you edit the Terragen Preferences about what file opens on startup of a new project ? If not, I would think you should probably reinstall Terragen.
For a new project the attached tgd is what you should get by default.
The object itself looks ok, it imports and renders ok in the default TGD.