C sharp - Validacion en Base de Datos....asp.net c#

<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>

            <ajaxToolkit:TextBoxWatermarkExtender ID="TextBox1_TextBoxWatermarkExtender"

                runat="server" BehaviorID="TextBox1_TextBoxWatermarkExtender" TargetControlID="TextBox1" />

protected void buttonSubmit_Click(object sender, EventArgs e)

{

    if (Page.IsValid)

    {

      labelMessage.Text = "Your reservation has been processed.";

    }

}

<script language="javascript">

function validateDate(oSrc, args)

{

  var iDay, iMonth, iYear;

  var arrValues;

  arrValues = args.Value.split("/");

  iMonth = arrValues[0];

  iDay = arrValues[1];

  iYear = arrValues[2];

  var testDate = new Date(iYear, iMonth - 1, iDay);

  if ((testDate.getDate() != iDay) ||

      (testDate.getMonth() != iMonth - 1) ||

      (testDate.getFullYear() != iYear))

  {

     args.IsValid = false;

     return;

  }

  return true;

}</script>