Excel spreadsheet generation results in "different file format than extension error" when opening in excel 2007

Question

The spreadsheet still displays, but with the warning message. The problem seems to occur because Excel 2007 is more picky about formats matching their extensions than earlier versions of Excel.

The problem was initially discovered by an ASP.Net program and produces in the Excel error "The file you are trying to open, "Spreadsheet.aspx-18.xls', is in a different format than specified by the file extension. Verify ...". However, when I open the file it displays just fine. I am using Excel 2007. Firefox identifies the file as an Excel 97-2003 worksheet.

Here is an ASP.NET page which generates the problem:

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Spreadsheet.aspx.cs" Inherits="Spreadsheet" %>

The code behind file looks like:

public partial class Spreadsheet : System.Web.UI.Page {
    protected void Page_Load(object sender, EventArgs e)
    {
        Response.ContentType = "application/vnd.ms-excel";
        Response.Clear();
        Response.Write("Field\tValue\tCount\n");

        Response.Write("Coin\tPenny\t443\n");
        Response.Write("Coin\tNickel\t99\n"); 

    } 

}

T

Answer 1

http://blogs.msdn.com/vsofficedeveloper/pages/Excel-2007-Extension-Warning.aspx

That is a link basically describing that MS knows about the problem your describe and that it cannot be suppressed from within ASP.NET code. It must be suppressed/fixed on the client's registry.