I have an ASP.Net MVC site that generates a Microsoft Excel 2003 XML formatted spreadsheet. The spreadsheet looks good, the controller and views both work, but the file won
Your problem may be in using the file extension .xml, which you're adding in your header.
My code that does this same thing does not have a file extension at all.
You might try dropping that .xml extension, or changing it to .xls or .csv.