Looks like a corrupted save, it happens with all software from time to time. Have you been saving in increments? It's a good idea to, so you can not only retreive most of your work from an earlier save, but if something you're working on heads in the wrong direction, you can always roll back.
Try and open your TGD file in a text editor, you may be able to get a look at what values you had in what nodes.