It's difficult to determine from the photos, but it appears that the program used to create the model is SketchUp. That program is well known for creating models which will not print.

If you're determined to stick with SketchUp, do some research about how to create manifold models from within the program. I tend to stay away from that program due to problems such as this.

It's possible that Meshmixer will solve the failed portions, or totally destroy the model! If you want to post the STL, I'll take a look at it to see how difficult a repair it is.