Hello Carl,
I'll try to help on this, if it continues not to work, please inform so Ankit can help further.
Starting from a fresh Kernel, ie Evalutation>Quit Kernel>StartKernel.
It works for me (WM 14, SM14) when I run this sequence of commands,
Text Line : Load the system modeling functionalities:
SystemModel;
Text LIne : Load the model diagram:
modelName = "ModelingPrinciples.Coffee.Exercises.Step1";
Now when you type the command below, on starting to type the Quotation mark, you will initially only see the leading Quote and the drop down menu of options to choose from. Once "Diagram" is selected the command is populated with "Diagram"
SystemModel[modelName, "]
Hope this was helpful,
John Burgers.