Export to excel code is not running give the error in vs2008

Question

private void export1_Click(object sender, EventArgs e)
{
if (dataGridView1.DataSource == null)
{
MessageBox.Show("Sorry nothing to export into excel sheet..", "", MessageBoxButtons.OK, MessageBoxIcon.Error);
return;
}
int rowsTotal = 0;
int colsTotal = 0;
int I = 0;
int j = 0;
int iC = 0;
System.Windows.Forms.Cursor.Current = System.Windows.Forms.Cursors.WaitCursor;
Excel.Application xlApp = new Excel.Application();

try
{

Excel.Workbook excelBook = xlApp.Workbooks.Add();
Excel.Worksheet excelWorksheet = (Excel.Worksheet)excelBook.Worksheets[1];
xlApp.Visible = true;
xlApp.Columns[3].Cells.NumberFormat = "@";
rowsTotal = dataGridView1.RowCount - 1;
colsTotal = dataGridView1.Columns.Count - 1;
var _with1 = excelWorksheet;
_with1.Cells.Select();
_with1.Cells.Delete();
for (iC = 0; iC <= colsTotal; iC++)
{
_with1.Cells[1, iC + 1].Value = dataGridView1.Columns[iC].HeaderText;
}
for (I = 0; I <= rowsTotal - 1; I++)
{
for (j = 0; j <= colsTotal; j++)
{
_with1.Cells[I + 2, j + 1].value = dataGridView1.Rows[I].Cells[j].Value;
}
}
_with1.Rows["1:1"].Font.FontStyle = "Bold";
_with1.Rows["1:1"].Font.Size = 12;

_with1.Cells.Columns.AutoFit();
_with1.Cells.Select();
_with1.Cells.EntireColumn.AutoFit();
_with1.Cells[1, 1].Select();
}
catch (Exception ex)
{
MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
finally
{
//RELEASE ALLOACTED RESOURCES
System.Windows.Forms.Cursor.Current = System.Windows.Forms.Cursors.Default;
xlApp = null;
}
}