Ajax Validator Callout extendar in asp.net

 

<asp:TextBox ID="txtWorkOrder" runat="server" MaxLength="10"></asp:TextBox>
<asp:RequiredFieldValidator ID="rfvworkorder" runat="server"
    ControlToValidate="txtWorkOrder" ErrorMessage="Please Select Work Order" Display="None" ValidationGroup="Request">
</asp:RequiredFieldValidator>
<ajax:ValidatorCalloutExtender ID="ValidatorCalloutExtender5" runat="server" PopupPosition="BottomLeft"
          TargetControlID="rfvworkorder" Width="180px" WarningIconImageUrl="~/images/icon_blue.png"   CssClass="CustomValidatorCalloutStyle">
</ajax:ValidatorCalloutExtender>