Try This
Response.Clear()
Response.Charset = ""
Response.AddHeader("content-disposition", "attachment;filename=report.xls")
Response.ContentType = "application/vnd.xls"
Response.Cache.SetCacheability(HttpCacheability.NoCache)
Dim stringWrite As New System.IO.StringWriter()
Dim htmlWrite As System.Web.UI.HtmlTextWriter = New HtmlTextWriter(stringWrite)
Excel_Word_details_view.RenderControl(htmlWrite)
Response.Write(stringWrite.ToString())
Response.End()
Catch ex As Exception