@Sameena Tara
Do you know which version of Excel created this .xls file?
Could other people open this file correctly?
If the pivot table was created in an older version of Excel but you want to open it through Excel for Microsoft 365 apps, this behavior may causes such error message.
Besides, if there is somthing wrong in Pivot Table, you would also see such error message.
It's recommended to back up this file first.
Go to Excel app > File > Formulas > Caculation Options, set "Manual" for Workbook calculation. Then open this file from Excel app to check this issue.
Change the format, such as .xlsx, re-open this file, create a new pivot tabe via Excel for Microsoft 365 apps.
Besides, you may refer to the article "Repair a corrupted workbook" to have a try.
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