Exporting into Excel

When I am exporting the data from Gridview to Excel, I am getting an error.

protected void Button1_Click(object sender, EventArgs e)

{

BindGrid();

}

private void BindGrid()

{

String Constr = "Data Source=WIN-A876U316VGA;integrated security=true;Initial Catalog=CUIDinfo";

SqlConnection con = new SqlConnection(Constr);

con.Open();

String SelectQuery = "Select * from ParcelInfo where RequestID =" + TextBox1.Text;

SqlCommand cmd = new SqlCommand(SelectQuery, con);

SqlDataAdapter da = new SqlDataAdapter(cmd);

DataSet ds = new DataSet();

da.Fill(ds);

GridView1.DataSource = ds.Tables[0];

GridView1.DataBind();

con.Close();

}

protected void Button2_Click(object sender, EventArgs e)

{

Response.Clear();

Response.Buffer = true;

Response.AddHeader("content-disposition", "attachment;filename=Download.xls");

Response.Charset = "";

Response.ContentType = "application/vnd.ms-excel";

using (StringWriter sw = new StringWriter())

{

HtmlTextWriter hw = new HtmlTextWriter(sw);

//To Export all pages

GridView1.AllowPaging = false;

GridView1.DataBind();

this.BindGrid();

//GridView1.HeaderRow.BackColor = Color.White;

foreach (TableCell cell in GridView1.HeaderRow.Cells)

{

cell.BackColor = GridView1.HeaderStyle.BackColor;

}

foreach (GridViewRow row in GridView1.Rows)

{

//row.BackColor = Color.White;

foreach (TableCell cell in row.Cells)

{

if (row.RowIndex % 2 == 0)

{

cell.BackColor = GridView1.AlternatingRowStyle.BackColor;

}

else

{

cell.BackColor = GridView1.RowStyle.BackColor;

}

cell.CssClass = "textmode";

}

GridView1.RenderControl(hw); "ERROR: HTTP exception was unhandled by user code"

//style to format numbers to string

string style = @"";

Response.Write(style);

Response.Output.Write(sw.ToString());

Response.Flush();

Response.End();

}

Could you please advise where am I going wrong???