with update panel ScriptManager.RegisterStartupScript( is not working

Dear all,

I am using update panel on my page  and  want to print a gridview.

If i remove the update panel, the below code is working..

Following is my code

Protected Sub btnPrint_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnPrint.Click  
            gvDetails.PagerSettings.Visible = False
            gvDetails.Visible = True
            gvDetails.AllowPaging = False
            gvDetails.DataSource = dt
            gvDetails.DataBind()
            Dim sw As New StringWriter()
            Dim hw As New HtmlTextWriter(sw)
            gvDetails.RenderControl(hw)
            Dim gridHTML As String = sw.ToString().Replace("""", "'").Replace(System.Environment.NewLine, "")
            Dim sb As New StringBuilder()
            sb.Append("<script type = 'text/javascript'>")
            sb.Append("window.onload = new function(){")
            sb.Append("var printWin = window.open('', '', 'left=0")
            sb.Append(",top=0,width=1000,height=600,status=0');")
            sb.Append("printWin.document.write(""")
            sb.Append(gridHTML)
            sb.Append(""");")
            sb.Append("printWin.document.close();")
            sb.Append("printWin.focus();")
            sb.Append("printWin.print();")
            sb.Append("printWin.close();};")
            sb.Append("</script>")
            ScriptManager.RegisterStartupScript(Me, Me.GetType(), "Print", sb.ToString(), True)        
            gvDetails.PagerSettings.Visible = True
            gvDetails.DataBind()
            gvDetails.Visible = False
     end sub

its showing me nothing

thanks

nick