ASP.NET Gridview to Export to Excel

Looks like you used code from this post https://stackoverflow.com/a/10412559/5786449

I tried the example from that post and it works for me. The only difference I can see is in your Response.ContentType and Response.AddHeader. Try getting rid of the white spaces in those parameters:

Response.ContentType = "application/vnd.ms-excel";
Response.AddHeader("content-disposition", "attachment;filename=MyFiles.xls");

One more thing, your code doesn't actually give you an Excel spreadsheet. It just writes out the GridView HTML markup. Many Excel programs are not expecting HTML in an XLS file and will throw an error when opening the file. If you want an actual Excel spreadsheet I would recommend looking into utilities like EPPlus http://epplus.codeplex.com/