I'm having trouble transferring datagridview to Excel

What is the reason I am getting the error like in datagridview below?

System.InvalidCastException: The COM object of type '' Microsoft.Office.Interop.Excel.ApplicationClass' could not be assigned to interface type 'Microsoft.Office.Interop.Excel._Application'. This operation failed because the QueryInterface call in the COM component for the interface with the IID '{000208D5-0000-0000-C000-000000000046}' failed with the following error: Error loading type library / DLL. (HRESULT exception returned: 0x80029C4A (TYPE_E_CANTLOADLIBRARY)). '

The code I wrote is:

saveFileDialog.InitialDirectory = "C:";
saveFileDialog.Title = "Save as Excel File";
saveFileDialog.FileName = "Data";
saveFileDialog.Filter = "Excel Files(2003)|*.xls|Excel Files(2007)|*.xlsx";

if (saveFileDialog.ShowDialog() != DialogResult.Cancel)
{
    Microsoft.Office.Interop.Excel.Application excelApp = new Microsoft.Office.Interop.Excel.Application();
    excelApp.Application.Workbooks.Add(Type.Missing);

    excelApp.Columns.ColumnWidth = 20;

    for (int i = 1; i < dgwReport.Columns.Count + 1; i++)
    {
        excelApp.Cells[1, i] = dgwReport.Columns[i - 1].HeaderText;
    }

    for (int i = 0; i < dgwReport.Rows.Count; i++)
    {
        for (int j = 0; j < dgwReport.Columns.Count; j++)
        {
            excelApp.Cells[i + 2, j + 1] = dgwReport.Rows[i].Cells[j].Value;
        }
    }

    excelApp.ActiveWorkbook.SaveCopyAs(saveFileDialog.FileName.ToString());
    excelApp.ActiveWorkbook.Saved = true;
    excelApp.Quit();
}

Using the posted code, I did not get the error you describe…

excelApp.Application.Workbooks.Add(Type.Missing);

This appears correct in creating a new Workbook. However, when it comes to writing the data to the workbook it appears to have a problem. The problem is that the code is writing the data to the excelApp and this is incorrect. The excelApp could have numerous workbooks open and each workbook could have numerous “worksheets.” You need to specify “where” (which worksheet in which workbook) you want to write to.

Since you are creating a new workbook, you need to “add” a new worksheet and write to that worksheet instead of the excelApp.

I tested the code below and it writes the data properly to a new worksheet in a new workbook.

saveFileDialog.InitialDirectory = "C:";
saveFileDialog.Title = "Save as Excel File";
saveFileDialog.FileName = "Data";
saveFileDialog.Filter = "Excel Files(2003)|*.xls|Excel Files(2007)|*.xlsx";

Microsoft.Office.Interop.Excel.Application excelApp = null;
Microsoft.Office.Interop.Excel.Workbook workbook = null;
Microsoft.Office.Interop.Excel.Worksheet worksheet = null;

try {
   if (saveFileDialog.ShowDialog() != DialogResult.Cancel) {
    excelApp = new Microsoft.Office.Interop.Excel.Application();
    workbook = excelApp.Application.Workbooks.Add(Type.Missing);
    worksheet = workbook.ActiveSheet;
    excelApp.Columns.ColumnWidth = 20;
    for (int i = 1; i < dgwReport.Columns.Count + 1; i++) {
      worksheet.Cells[1, i] = dgwReport.Columns[i - 1].HeaderText;
    }
    for (int i = 0; i < dgwReport.Rows.Count; i++) {
      for (int j = 0; j < dgwReport.Columns.Count; j++) {
        worksheet.Cells[i + 2, j + 1] = dgwReport.Rows[i].Cells[j].Value;
      }
    }
    excelApp.ActiveWorkbook.SaveCopyAs(saveFileDialog.FileName.ToString());
    excelApp.ActiveWorkbook.Saved = true;
    workbook.Close();
    excelApp.Quit();
  }
}
catch (Exception ex) {
  MessageBox.Show("Excel write error: " + ex.Message);
}
finally {
  // release the excel objects to prevent leaking the unused resource
  if (worksheet != null)
    Marshal.ReleaseComObject(worksheet);
  if (workbook != null)
    Marshal.ReleaseComObject(workbook);
  if (excelApp != null)
    Marshal.ReleaseComObject(excelApp);
}