System.ApplicationException: Invalid file format.
at C1.C1Excel.C1XLBook.r(String A_0, Boolean A_1)
at C1.C1Excel.C1XLBook.Load(String fileName, FileFormat format, Boolean fillSheets)
at C1.C1Excel.C1XLBook.Load(String fileName, Boolean fillSheets)
According to the help, Excel 8.0 is supposed to be supported. And I can open the file just fine with Excel.