Follow up:
Joe sent me his file, it turned out there was a "lost" chart on the sheet
with all of its Series having invalid references. In Excel 2007 copying a
sheet with such a chart led to failure to reconcile the invalid references
and the automation error Joe described in this thread. Deleting the chart
resolved the copy sheet problem.
The chart would have become "lost" as a result of deleting all the rows that
contained it, making its height zero and effectively not visible.
It wasn't obvious!

Peter T