alert script is not working in grideview control in Iframe tag in asp.net

Protected Sub Delete_onGridRow_Click(ByVal sender As Object, ByVal e As EventArgs)
        Try
            ostate = New BLstate

            str = DirectCast(sender, System.Web.UI.WebControls.ImageButton).CommandName.ToString
            With ostate
                .stateid = str
            End With

            result = state.state_delete(ostate)

            If result > 0 Then
                gvList.DataSource = state.Listview(txtstate.Text, ddstateStatus.SelectedValue)
                gvList.DataBind()
                'Page.ClientScript.RegisterClientScriptBlock(Me.GetType, "alert", "alert('item not deleted');", True)
                'Page.ClientScript.RegisterStartupScript(Me.GetType, "alert", "showDialog('Warning','Item not deleted.','warning');", True)
                'Response.Write("item not deleted")
                Response.Write("<script type=text/javascript>alert('item not deleted')</script>")
                NoDataLabel.Text = "item not deleted"
            End If

        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub