意外令牌<Ajax

Unexpected token < {stack: (...), message: "Unexpected token <"}

I would like to call an Ajax function but i got this error instead ...

<script type="text/javascript">
    $(document).ready(function() {
    var interval = setInterval(function(){
        $.ajax({
            url     :'index.php?module=Page&action=Mandats',
            type    : 'post',
            timeout : 3000,
            data    : $(this).serialize(),
            dataType: 'json',
            success : function (data, status, xhr){ 
                alert(status);
                },
            error   : function (xhr, status, error){
                console.log(xhr);
                console.log(status);
                console.log(error);
            }
        });
    }, 1000);
    });
</script>

Do you know why that ?