I get this message intermittently with Microsoft Web Expression 3:
The contents of a FrontPage component have been modified. These contents will be overwritten when you save this page.
I have read kb/219873, but it did not help.
It seems that Include pages are the cause of this error message.
While I have not come up with a definitive answer, I found that posting in the specialist Expression Web forum helped. There are good people dedicated to Expresson over there. (Just as there are wonderful people at this site).