Locate the error

Hi,
To this Stacktrace

Exception: The specified package is invalid. The main part is missing.    at DocumentFormat.OpenXml.Packaging.OpenXmlPackage.Load()
   at DocumentFormat.OpenXml.Packaging.OpenXmlPackage.OpenCore(String path, Boolean readWriteMode)
   at DocumentFormat.OpenXml.Packaging.SpreadsheetDocument.Open(String path, Boolean isEditable, OpenSettings openSettings)
   at DocumentFormat.OpenXml.Packaging.SpreadsheetDocument.Open(String path, Boolean isEditable)
   at App12.Program.ReadFile(String par_File)

which line should be with the error? How to further find out reason to such error? But now the Stacktrace is NOT pointing out which line is having PROBLEM!

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Many Thanks & Best Regards, Hua Min