ASP.NET

private void DrillDown(DataTable drillDown)
    {
        try
        {
            Page.Session.Add("excelTable", drillDown);
            Page.Session.Add("excelName", "DrillDownClaimsReport");
            Page.Session.Add("returnPageAfterExport", "../Reports/ClaimReport.aspx");
            Response.Redirect("../Export/DataTableToExcel.aspx");
        }
        catch (Exception err)
        {
            lblError.Text = err.Message;
        }
    }

using System;
using System.IO;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class Export_DataTableToExcel : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        DataTable excelTable = new DataTable();
        String excelName = String.Empty;
        String returnPage = String.Empty;
        excelTable = (DataTable)Page.Session["excelTable"];
        excelName = (string)Page.Session["excelName"];
        returnPage = (string)Page.Session["returnPageAfterExport"];
        ExportDataTableToExcel(excelTable, excelName, returnPage);
    }

    private void ExportDataTableToExcel(DataTable table, String fileName, String returnPage)
    {
        // Export function to excel. Should work without any Excel dll's now, so stand-alone.

        Response.Clear();
        Response.AddHeader("content-disposition", String.Format("attachment;filename={0}.xls", fileName));

        Response.ContentType = "application/ms-excel";
        //Response.ContentType = "application/vnd.ms-excel";
        Response.Charset = "iso-8859-1";
        String Combineer = String.Empty;

        String sep = String.Empty;
        foreach (DataColumn dc in table.Columns)
        {
            Combineer += sep + dc.ColumnName.Replace("_", " ").Replace("occurrence date", "Date of Loss");
            sep = "\t";
        }
        Combineer += "\n";

        int i;
        foreach (DataRow dr in table.Rows)
        {
            sep = String.Empty;
            for (i = 0; i < table.Columns.Count; i++)
            {
                Combineer += sep + dr[i].ToString();
                sep = "\t";
            }
            Combineer += "\n";
        }
        Response.Write(Combineer);
        Response.End();
        Page.Session.Remove("excelTable");
        Page.Session.Remove("excelName");
        Page.Session.Remove("returnPageAfterExport");
        Response.Redirect(returnPage);
    }
}