May need this in the Page Directive: EnableEventValidation = "false"

Public Overrides Sub VerifyRenderingInServerForm(ByVal control As Control)

'**********************************************************

'**********************************************************

'Mandatory to have this empty sub to avoid runtime error

'**********************************************************

'**********************************************************

End Sub

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles cmdPrint.Click

Response.Clear()

Response.Buffer = True

Response.ClearContent()

Response.ClearHeaders()

Response.Charset = ""

Dim FileName As String = "MyExcelFile" + DateTime.Now + ".xls"

Dim strWriter As New Stringwriter

Dim HtmlTextWriter As HtmlTextWriter = New HtmlTextWriter(strWriter)

Response.Cache.SetCacheability(HttpCacheability.NoCache)

Response.ContentType = "application/vnd.ms-excel"

Response.AddHeader("Content-Disposition", "attachment;filename=" + FileName)

gvDetail.GridLines = GridLines.Both

gvDetail.HeaderStyle.Font.Bold = True

gvDetail.RenderControl(HtmlTextWriter)

Response.Write(strWriter.ToString())

Response.End()

End Sub