X5 and Search "no topics found"

A .chm help file I've created with X5 always returns message "No Topics Found" when anything is entered in the search dialogue.

I haven't used Robo much recently, so checked an old project chm (2002 vintage) to see if I could enter any word seen on a page and have it found - and the search worked fine.
I then opened this old project up in X5, saved it, recompiled, and now the search does not work.

Any clues what settings I may have wrong.
Have X5 installed locally - no servers involved as mentioned in other posts.
Just turned IE7 security to Medium - no change


Thanks