Unavailable Fonts error

[Karen Robbins]

A file (generated file from a plain text source) keeps displaying the 
"unavailable fonts" error each time it opens.

I've run Silicoin Prairie's Paragraph Tools on this file, and the 
only font it finds in the file is HelveticaNeueLT Std--exactly as it 
should be. I've checked the master pages (four)--no hidden text 
boxes; and the reference page (one)--nothing else there.

What could the error be pointing to?

Thanks,
Karen