"Create a DTD" cannot find XML application

I'm working with the opening chapters in the FM8 Structure Application Developer Guide and I'm stuck at page 39/40.  I've created an EDD, altered the structapps.fm file and defined the read/write rules (which I saved with the imaginative name "ReadWriteRules".)

Following the instructions I went back to the EDD and added the StructuredApplication element, so it looks like this:

Element Catalog

Version

StructuredApplication       ReadWriteRules.fm

However, when I select StructureTools>Save as DTD... first off, the "Save As Type:" doesn't offer .dtd as an option.  So I typed "DTD Test.dtd" into the file name and clicked Save.  But I get an error message saying "Application "ReadWriteRules.fm" does not exist"

In the Define the read/write rules section, it doesn't specify, so I saved it to the default (as an .fm file.)  However, the Create a DTD section talks about the XML application, so I tried saving it as "ReadWriteRules.xml" and changing the EDD to "ReadWriteRules.xml", but I still get the same error message.

Any suggestions would be appreciated!