Your questions are well beyond the scope of this article. If time allows I may discuss this topic at a future time.

I have gotten that error a few times, for no reason I could detect. When I recovered the contents of the workbook, I didn’t notice any problem. Maybe in your situation the chart was outside of Excel 2007’s comfort zone. If you haven’t applied any service pack, I would suggest installing SP1. I haven’t installed SP2 yet, because there have been a lot of complaints related to it. Perhaps hold off on that one to see if the complaints subside.

However I still have the following problem:
When I successfully create a secondary axis [because I want to overlay a moving average on the bars] and save the workbook the chart is unrecoverable when I try to reload the workbook later. I get a message saying “Excel found unreadable content in ’stock.chart.object.xlsm’. Do you want to recover the contents of this workbook?” When I reply ‘yes’ the spreadsheet is displayed without the chart. A ‘no’ reply loses the entire workbook. I have tested it enough in various ways to feel confident that it is probably the secondary axis addition that is the problem.
Any suggestions will be much appreciated. Someone suggested a ’service pack update’ might help – whatever that is? I have Excel 2007.