Error! Not a valid heading level in TOC entry on page 1

My company's house style is to do tables of contents using TC codes - which usually works fine and we've got some macros to update them all at once etc.  One document however has the wording "Error! Not a valid heading level in TOC entry on page 1" at the top of the table of contents - and no matter what I do it won't go away.  Has anyone seen this before?  I've checked all the bookmarks, all the formatting, all the styles - everything I can think of.  I've replaced the TOC is