I need to get a value from another page. But I get this error with the following code. How can I fix it?

$(document).ready(function() { 
    $("[name='submit']").click(function() { 
        $.ajax({
            type: "POST",
            data: $(".form-signup").serialize(),
            url: "external.asp", 
            success: function(output) { 
            alert(output.getResponseHeader("Content-Length"));,
            error: function(output) {
            $('.sysMsg').html(output);
            }
        }); 
    }); 
});