I would suggest putting this in a before save macro rather than an on open macro. This means the change will be visible more immediately, it also means the summary field would be populated if the workbook was sent to another who has security on high (as default).
Try this:
You may want to think about when you want this to run... when you change something on the sheet, when you open or close the workbook, when you save it... when you type "Gary is a big loser" in cell A14 on page 8... (all very easy to do!)
The built in document properties are easy to refer to by index number but I find it much easier to see what you've done this way.
Finally, check that your sheet is named "Sheet1" if not, amend as apt. The code I provide definitely works for me.
HTH
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