Index markers not showing in generated index

[Pete Rourke]

I have created an index marker for a primary: secondary, and the marker
appears on the page, and shows correctly in the marker box, but when update
and generate indexes is run the secondary does not show. There are lots of
secondary items in the primary. 

I'm a FM newbie FM8.0p266, and may have missed a fundamental principle for
indexing.

Suggestions?

 

Pete