Ajax状态200返回错误

I am using ajaxForm, but this one is acting strange. I am calling:

$('#myForm').ajaxForm({
  type: "POST",
  dataType: 'json',
  success: function (json) {

  },
  error: function (jqXHR, textStatus, errorThrown) {

  }
});

The form calls a function which returns in the end:

$arrReturn['LNK'] = $fn;
print json_encode($arrReturn);

But I'm landing in the error with the correct return values:

Array{"LNK":"1437640345.xlsx"}

I've tried to remove the dataType, set a header in my called function, build the json String all by myself, but nothing changed anything. Am I doing something wrong?

Use following

$.ajax({
          type: "POST",
          url: url,
          data: data,
          success: function (res) {
           // your process
           }
           ,
           error: function (jqXHR, textStatus, errorThrown) {

            }
       });