Thank you for your ideas.

In this particular case I was less interested in a workaround than in the cause. To resolve the issue I ended up deleting the grid and recreating it (see my previous message ID 1117241).

I believe that the grid definition rows in the .SCX/.SCT must have had some non-obvious corruption. Over the years this grid has had its columns extensively added to, removed, and the columns' ColumnOrder changed.

Thanks again.

Spence