How to trigger asp.net customvalidator with javascript

I am trying to trigger asp.net custom validator with java script but it is not triggering. Other validators such as required field validators are getting triggered from the below-shown code. Can anyone tell me what is wrong in the below code or why it is not triggering

<script type="text/javascript">
         function CheckValidation(btn) {
             var valid = false;
             if (Page_ClientValidate('RtRegValGrp')) {

                 alert('valid');
                 __doPostBack(btn.name, "");

             }
             else {
                 alert('not valid');
             }
         }
             </script>
     <asp:TextBox ID="txtCompanyName" runat="server" MaxLength="100"></asp:TextBox>
                                        <asp:RequiredFieldValidator ValidationGroup="RtRegValGrp" ID="RequiredFieldValidator1" runat="server" ErrorMessage="Company name is required !"
                                            ControlToValidate="txtCompanyName" ForeColor="red" Display="Dynamic" />
         <asp:CustomValidator ValidationGroup="RtRegValGrp" ID="txtCompanyNameValidator" ForeColor="Red" OnServerValidate="BlackListValidator" Display="Dynamic" ControlToValidate="txtCompanyName" runat="server">
                                        </asp:CustomValidator>

         <asp:Button ID="Button1" runat="server" CssClass="goldBtn" Text="SUBMIT" OnClientClick="CheckValidation(this); return false;" OnClick="Button1_Click" />

//server side code
     protected void BlackListValidator(object source, ServerValidateEventArgs args)
        {
            args.IsValid = false;
        }