Trying to make multiple dependent drop down list with dynamic ranges

I want to set up two drop-down lists. The selection you make determines what you get in the second drop-down. The trouble is, I want the ranges to be dynamic, so I can add more materials to the lists without having to rewrite the code. I have successfully done it with a static range.

This website has exactly the example I'm looking for at the very bottom of the page.
http://www.contextures.com/xlDataVal02.html
The trouble is, I haven't been able to make it work. I even tried recreating her example, and it wouldn't work. It says that it is referencing an error, and the drop down doesn't show any options even when the first column is filled in correctly.