Error message when trying to apply master page

I think I broke something and need help figuring out how to fix it. I'm new to FrameMaker so I'm hoping this is an easy fix.

My document has 14 chapters plus two appendices. The chapters all follow the same basic master page (with room for 1.25-inch side head), while the appendices don't have a side head. At some point, I went to copy a new paragraph style from one chapter to all the other chapters, but I inadvertently copied all of the formats ... from one of my appendices. Now all of my chapters have lost the side-head master page (along with the chapter-specific headers and footers).

I re-created the master page for one of my chapters and went to re-apply it to all of the other chapters, but I'm now getting the error message, "No master pages applied because the MasterPageMaps table contains no mapping information." I get this message in two situations:

• If I try to apply the master page at the book level, to all of my chapters.
• In one instance, where I re-created the master page (a second time) in another chapter and tried to apply it to that chapter.

I am following the instructions in the help content, so I'm wondering if this is a bug rather than a newbie error. I've researched this community and have found a couple of posts on this same error message, but the answers there don't seem to apply to my situation.

For reference, I'm using unstructured FrameMaker version 15.0.4.751.