Валидатор формы "удаленный" url-адрес не вызывает webmethod

 I am facing issue for calling webmethod from remote validator in form validation.Please help me to resolve this issue.

Please check my code:

**

JQuery:

txtUsername: {
                    verbose: false,
                    validators: {
                        notEmpty: {
                            message: '<%=Resources.LocalizedText.UserNameRequired%>'
                        },
                        stringLength: {
                            min: 6,
                            max: 30,
                            message: '<%=Resources.LocalizedText.UserNameAtleastSixChars%>.'
                        },
                        regexp: {
                            regexp: /^[a-zA-Z0-9_\.]+$/,
                            message: '<%=Resources.LocalizedText.InvalidCharactersOnlylettersNumAndUnderscores%>'
                        },
                        remote: {
                            url: '/BackOfficeOperations/HMS/SimpleHMS.aspx.cs/checkUsername',
                            type: 'POST',

                            message: '<%=Resources.LocalizedText.UserNameAlreadyExists%>',
                            delay: 1000
                        }
                    }



                }

code

[WebMethod]
   public static void checkUsername(string txtUsername)
   {
       var tsvc = new TenantService();
       if (tsvc.UserNameExists(txtUsername))
           HttpContext.Current.Response.Write("{\"valid\": false}");
       else
           HttpContext.Current.Response.Write("{\"valid\": true}");
   }

HTML

<input class="form-control" name="txtUsername" />