the file you are trying to open is in a different format than specified by the file extension in Asp.Net

calendar_today Asked Apr 22, 2013
thumb_up 19 upvotes
history Updated April 16, 2026

Question posted 2013 · +14 upvotes

the file you are trying to open is in a different format than specified by the file extension c# error when trying to open file in excel.

Here is my code

public ActionResult Export(string filterBy)
{
    MemoryStream output = new MemoryStream();
    StreamWriter writer = new StreamWriter(output, Encoding.UTF8);

    var data = City.GetAll().Select(o => new
    {
        CountryName = o.CountryName,
        StateName = o.StateName,
        o.City.Name,
        Title = o.City.STDCode
    }).ToList();
    var grid = new GridView { DataSource = data };
    grid.DataBind();
    var htw = new HtmlTextWriter(writer);

    grid.RenderControl(htw);

    writer.Flush();
    output.Position = 0;

    return File(output, "application/vnd.ms-excel", "test.xls");

}

when am trying to open excel i get this error

the file you are trying to open is in a different format than specified by the file extension

enter image description here

After clicking on Yes the file open properly. but i don’t want this msg to appear.

Accepted answer +19 upvotes

I have used CloseXML to solve the problem.

public static void ExportToExcel(IEnumerable<dynamic> data, string sheetName)
{
    XLWorkbook wb = new XLWorkbook();
    var ws = wb.Worksheets.Add(sheetName);
    ws.Cell(2, 1).InsertTable(data);
    HttpContext.Current.Response.Clear();
    HttpContext.Current.Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
    HttpContext.Current.Response.AddHeader("content-disposition", String.Format(@"attachment;filename={0}.xlsx",sheetName.Replace(" ","_")));

    using (MemoryStream memoryStream = new MemoryStream())
    {
        wb.SaveAs(memoryStream);
        memoryStream.WriteTo(HttpContext.Current.Response.OutputStream);
        memoryStream.Close();
    }

    HttpContext.Current.Response.End();
}

Installed ClosedXML in my project using Nuget Package Manager.

External references cited (2)

Excel VBA objects referenced (5)

  • City.Name — Refer to Named Ranges
  • City.Name — Invalid procedure name error
  • HttpContext.Current — Create a DAO Recordset from a table in the current database
  • HttpContext.Current — Find the current position in a DAO Recordset
  • String.Format — PivotTable.HasAutoFormat property (Excel)pivottable-hasautoformat-property-excel-638f892d-7dc9-314c-efaf-ee724b9f86f5

Top excel Q&A (6)

+19 upvotes ranks this answer #30 out of 167 excel solutions on this site — top 18%.
excel