"Couldn't find tag"

I just created a new paragraph style called "Note" that puts the text into a side head. If I click on the note, I keep getting a message that says "Couldn't find tag: Note." I've tried deleting the paragraph style, closing and re-opening FrameMaker, and creating the note style all over again, but that doesn't seem to help.

I thought perhaps it was the "Side Head" property that was causing the error, so I went into the paragraph designer and tried to change it back to "In Column." This doesn't seem to make any difference -- I'm still getting the error message.

I've done some research and found something on this happening in Structured, but I'm using Unstructured. Does anyone know if this is a bug?