ASP.NET - CustomValidator's ServerValidate event fires twice

in case when CustomValidator's ServerValidate event fires twice (or more) - delete all commented out javascript and html code

In java anything like
//        function SetFocusHome() {
//            document.getElementById('<%= txtHome.ClientID %>').focus();
//        }

in html

<%--        <asp:RequiredFieldValidator ID="ValidateCallBackDate" runat="server" ErrorMessage=" select a call back date."
            ControlToValidate="txtCB" CssClass="errorMessage" Display="None"></asp:RequiredFieldValidator>--%>