export to excel from datadrid - you can only call RegisterForEventValidation for render ()

i am using this code for export to excel from datagrid
Partial Class exportToExcel
    Inherits System.Web.UI.Page

    Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        '// Disable paging
        GridView1.AllowPaging = False

        '// exluded columns arraylist
        Dim defaultExcludedColumns As New ArrayList()

        '// Always exclude these columns
        defaultExcludedColumns.Add("")

        '// Send to base Excel export method
        ExportGridView(GridView1, "Excel-Name", defaultExcludedColumns)

        '// Rebind with paging enabled
        GridView1.AllowPaging = True
    End Sub


    '/// <summary>
    '/// Export GridView data to Excel.
    '/// </summary>
    '/// <param name="grdView">GridView control to export.</param>
    '/// <param name="filename">Filename of excel spreadsheet.</param>
    '/// <param name="excludedColumnList">ArrayList of columns to exlude.</param>
    Sub ExportGridView(ByVal grdView As GridView, ByVal filename As String, ByVal excludedColumnList As ArrayList)
        '// Clear response content & headers
        Response.Clear()
        Response.ClearContent()
        Response.ClearHeaders()


        '// Add header
        Response.AddHeader("content-disposition", "attachment;filename=" + filename + ".xls")
        Response.Charset = String.Empty
        Response.Cache.SetCacheability(System.Web.HttpCacheability.Public)
        Response.ContentType = "application/vnd.xls"

        '// Create stringWriter
        Dim stringWrite As New System.IO.StringWriter()

        '// Create HtmlTextWriter
        Dim htmlWrite As New HtmlTextWriter(stringWrite)


        '// Remove controls from Column Headers
        If (grdView.HeaderRow IsNot Nothing And grdView.HeaderRow.Cells IsNot Nothing) Then
            Dim ct As Integer
            For ct = 0 To grdView.HeaderRow.Cells.Count - 1 Step ct + 1
                ' Save initial text if found
                Dim headerText As String = grdView.HeaderRow.Cells(ct).Text

                ' Check for controls in header
                If grdView.HeaderRow.Cells(ct).HasControls() Then
                    ' Check for link button
                    If grdView.HeaderRow.Cells(ct).Controls(0).GetType().ToString() = "System.Web.UI.WebControls.DataControlLinkButton" Then
                        ' link button found, get text
                        headerText = (CType(grdView.HeaderRow.Cells(ct).Controls(0), LinkButton)).Text
                    End If

                    ' Remove controls from header
                    grdView.HeaderRow.Cells(ct).Controls.Clear()
                End If

                ' Reassign header text
                grdView.HeaderRow.Cells(ct).Text = headerText
            Next

        End If
        '// Remove footer
        If (grdView.FooterRow IsNot DBNull.Value) Then

            grdView.FooterRow.Visible = False
        End If

        '// Remove unwanted columns (header text listed in removeColumnList arraylist)
        Dim field As DataControlField
        For Each field In grdView.Columns

            If (excludedColumnList.Contains(field.HeaderText)) Then

                field.Visible = False
            End If
        Next

        '// Call gridview's renderControl
        grdView.RenderControl(htmlWrite)

        '// Write Response to browser
        Response.Write(stringWrite.ToString())

        Response.End()
    End Sub

    Public Overrides Sub VerifyRenderingInServerForm(ByVal control As System.Web.UI.Control)
        'MyBase.VerifyRenderingInServerForm(control)

    End Sub

End Class

BUT I HAVE THIS ERROR:
you can only call RegisterForEventValidation for render ()
view attached please
i am working in vs2005 and vb.net
exportarERROR.jpg