问wordpress admin-ajax.php文件中出现Ajax“错误请求”错误400

EN

  function checkusername(){
    var u = _("username").value;
    if(u != ""){
        _("unamestatus").innerHTML = 'checking ...';
        var ajax = ajaxObj("POST", "<?php echo admin_url('admin-ajax.php'); ?>");
        ajax.onreadystatechange = function() {
            if(ajaxReturn(ajax) == true) {
                _("unamestatus").innerHTML = ajax.responseText;
            }
        }
        ajax.send("usernamecheck="+u);
    }
}
function signup(){
    var u = _("username").value;
    var e = _("email").value;
    var p1 = _("pass1").value;
    var p2 = _("pass2").value;
    var fn = _("fname").value;
    var ln = _("lname").value;
    var m = _("major").value;
    var phone = _("phone").value;
    var blazeid = _("blazerid").value;
    var status = _("status");
    if(p1 != p2){
        status.innerHTML = "Your password fields do not match";
    }else {
        _("signupbtn").style.display = "none";
        status.innerHTML = 'please wait ...';
        var ajax = ajaxObj("POST", "<?php echo admin_url('admin-ajax.php'); ?>");
        ajax.onreadystatechange = function() {
            if(ajaxReturn(ajax) == true) {
                if(ajax.responseText != "signup_success"){
                    status.innerHTML = ajax.responseText;
                    _("signupbtn").style.display = "block";
                } else {
                    window.scrollTo(0,0);
                    _("signupform").innerHTML = "OK "+u+", check your email inbox and junk mail box at <u>"+e+"</u> in a moment to complete the sign up process by activating your account. You will not be able to do anything on the site until you successfully activate your account.";
                }
            }
        }
        ajax.send("u="+u+"&e="+e+"&p="+p1+"&fn="+fn+"&ln="+ln+"&m"+m+"&phone"+phone+"&blazeid"+blazeid);
    }
}