How to add new page size to stylesheet?

There is a request to add c-size drawings to our manuals. I would like to know how to add it to my style sheet.

This is what I have done so far

In styler:

1. Make a copy of the existing stylesheet.

2.  I go to Page Type, I locate the the foldout (11 X 17) that we currently have defined and I copy all the types and rename them to foldout2.

3. I then go to page set, locate the foldout page set, copy it and rename it foldout2 page set. In the page size I change the page size to C size. Under page types I change the page types to reference the new foldout2 page types.

4. Keep the page region the same

5. Click on the element foldout, copy and paste rename to foldout2. It states that this new element is not in my document type. I cannot figure out where this is. Is this my servicemanual.dtd? I have searched the file for the word foldout but it is not in there. I read through the adding new elements to your stylesheet article in the help, but it does not cover the error message a20377.

Thanks

Bryon