Error while saving excel file after updating value

Question

I am using Excel Interop library for reading and writing excel sheet.When i try to write and save workbook by Save() method it gives,

Exception from HRESULT: 0x800A03EC

Although Saveas() and SaveCopyAs() method works fine.I want to update same file used for read. Below is my code:-

 excelApplication = new Excel.Application();
                        excelApplication.DisplayAlerts = false;
                        // excelApplication.ScreenUpdating = true;
                        excelApplication.Visible = false;
                        excelWorkbook = excelApplication.Workbooks.Open(filePath,
                        Type.Missing, false, Type.Missing, Type.Missing,
                        Type.Missing, true, Type.Missing, Type.Missing,
                        true, Type.Missing, Type.Missing, Type.Missing,
                        Type.Missing, Microsoft.Office.Interop.Excel.XlCorruptLoad.xlExtractData);

                        dict = new Dictionary<string, Excel.Worksheet>();

                        foreach (Excel.Worksheet worksheet in excelWorkbook.Worksheets)
                        {
                            dict.Add(worksheet.Name, worksheet);
                            Excel.Worksheet sheet = dict[worksheet.Name];
                        }
                        Excel.Worksheet sheetobj = dict["Risk Register"];
                         //sheetobj.Cells[10, 4]
                        ((Excel.Range)sheetobj.Cells[10, 4]).Value2 =123;

                        excelWorkbook.Save();