问让jQuery.ajax将响应解释为错误

EN

$.ajax({
    type:'POST',
    url:'/ajax/registration.php',
    data:{formData: formData},
    success:function(data){eformDef.forms.registration.success(data);},
    error:function(data){eformDef.forms.registration.success(data);}
});

$data = $_POST['formData'];
$firstName = mysql_real_escape_string($data['first name']);
$lastName = mysql_real_escape_string($data['last name']);
$email = mysql_real_escape_string($data['email address']);
$password = mysql_real_escape_string($data['password']);


mysql_query("INSERT INTO users (first_name, last_name, email, password) VALUES ('$firstName', '$lastName', '$email', '$password')") or die(mysql_error());