Download .xlsx file using Response.TransmitFile()

I can't definitely say that there's anything wrong with your approach, but I'll just share some observations from doing something similar.

Headers are Pascal Case, most browsers shouldn't care but I would change your content-disposition to Content-Disposition. Changing the Charset shouldn't be necessary or relevant. Your content type should be fine, I would only use application/vnd.openxmlformats-officedocument.spreadsheetml.sheet and .xlsx if that is actually the content of the file, otherwise stick with application/vnd.ms-excel and .xls.

Another thing you should consider is sending the browser the Content-Length:

Response.AddHeader("Content-Length", new System.IO.FileInfo("FileName.xlsx").Length);

Also have you tried this with multiple browsers? Just wondering if it's a vendor-specific problem.

As a last ditch effort, you can set your Content-Type to application/octet-stream, and any browser should offer to download it, and then most browsers will let you open it after it's downloaded based on the extension.

use this

HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment;filename=\"filename + ".zip" + "\"");                Response.TransmitFile(zipPath);                Response.Flush();                Response.Close();                Response.End();

in your code is

Response.AddHeader("content-disposition", "attachment;filename=\FileName.xlsx\");

Try like this

public void DataTableToExcel(DataTable dt, string Filename){    MemoryStream ms = DataTableToExcelXlsx(dt, "Sheet1");    ms.WriteTo(HttpContext.Current.Response.OutputStream);    HttpContext.Current.Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";    HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment;filename=" + Filename);    HttpContext.Current.Response.StatusCode = 200;    HttpContext.Current.Response.End();}public static MemoryStream DataTableToExcelXlsx(DataTable table, string sheetName){    MemoryStream result = new MemoryStream();    ExcelPackage excelpack = new ExcelPackage();    ExcelWorksheet worksheet = excelpack.Workbook.Worksheets.Add(sheetName);    int col = 1;    int row = 1;    foreach (DataColumn column in table.Columns)    {        worksheet.Cells[row, col].Value = column.ColumnName.ToString();        col++;    }    col = 1;    row = 2;    foreach (DataRow rw in table.Rows)    {        foreach (DataColumn cl in table.Columns)        {            if (rw[cl.ColumnName] != DBNull.Value)                worksheet.Cells[row, col].Value = rw[cl.ColumnName].ToString();            col++;        }        row++;        col = 1;    }    excelpack.SaveAs(result);    return result;}