I watched Martha Zink's video, and compared her example file to your own, and there are some differences.
The big difference is that the example file seems to be a different from the one used in the video. It would seem from the comments on the page, the example file was added later. The most notable thing is the lack of a Popover in the example file where you can choose the type of file to be inserted. Nevertheless, the file still works the way it should without it.
The other differences are between the example file, and your attempt of implementing it. I believe you left off some needed fields, and / or renamed fields and layouts, that can be confusing you and me. it is hard to see what went wrong.
You will learn that when adapting a solution to your own files, you need to copy everything exactly as the example file has it. This might mean to temporary rename things in YOUR file such as Tables. Here is a Checklist for moving files that you might find helpful because it gives the order on how you should move things.
Do not try to rename the fields, relationships, etc., until you are sure it works in your file as expected. Once you have it working, you can then make name changes to suit your file. When naming things, try to follow a naming conventions such as suggested in http://filemakerstandards.org/display/cs/Overview