Error While Export To Excel in sharepoint 2010 Programmatically - sharepoint

Question

The file you are trying is in a different format than specified by the file extension.Verify that the file is not corrupted and is from a trusted source before opening the file.Do you want to open the file now?
and this 'export to excel' dead the events on the page.
Here is my code
public void ExportToExcelitems(DataTable dt, string fileNameWithoutExt)
{
if (dt.Rows.Count > 0)
{
string filename = fileNameWithoutExt + ".xls";
System.IO.StringWriter tw = new System.IO.StringWriter();
System.Web.UI.HtmlTextWriter hw = new System.Web.UI.HtmlTextWriter(tw);
var dgGrid = new GridView();
dgGrid.DataSource = dt;
dgGrid.DataBind();
dgGrid.HeaderRow.BackColor = System.Drawing.Color.White;
dgGrid.HeaderRow.BackColor = System.Drawing.Color.White;
foreach (GridViewRow row in dgGrid.Rows)
{
row.BackColor = System.Drawing.Color.White;
foreach (TableCell cell in row.Cells)
{
if (row.RowIndex % 2 == 0)
{
cell.BackColor = dgGrid.RowStyle.BackColor;
}
else
{
cell.BackColor = System.Drawing.Color.LightGray;
}
}
}
dgGrid.AutoGenerateColumns = false;
dgGrid.RenderControl(hw);
HttpContext.Current.Response.ContentType = "application/vnd.ms-excel";
HttpContext.Current.Response.AppendHeader("Content-Disposition", "attachment; filename=" + filename + "");
this.EnableViewState = false;
HttpContext.Current.Response.Write(tw.ToString());
HttpContext.Current.Response.Flush();
HttpContext.Current.Response.Close();
}
}

Answer 1

I think you should consider using OpenXML (or more specfically ClosedXML) to build a modern Excel file with the xlsx extension.
Open XML SDK: https://learn.microsoft.com/en-us/office/open-xml/open-xml-sdk
Closed XML (nuget): https://www.nuget.org/packages/ClosedXML/
Code Samples: https://github.com/ClosedXML/ClosedXML/wiki/Deliver-an-Excel-file-in-ASP.NET