I'm really enjoying this training, Rob!
I've downloaded the .zip file and extracted everything. In the zip file there's two folders, one is Calculator Solution and the other is Calculator Solution End. It looks to me as though Calculator Solution is the solution without any of the unit testing projects. Calculator Solution End requires me to connect to your TFS repository before I can open the solution. I'll give it a try, and I hope it will only allow me to connect as a guest.
I opened the Calculator Solution End solution, it did ask to get connected to your TFS. Here's the error it gave me:
But I think it's OK.