toi kết hợp jquery + ajax + json trong viễt code thì gặp lỗi parseJSON: filter failed
đoạn code thế này:

Mã:
<script src="libs/jQuery/jquery.js" language="javascript" type="text/javascript"></script>
<script src="libs/jQuery/json.js" language="javascript" type="text/javascript"></script>
<script src="libs/jQuery/ajax.js" language="javascript" type="text/javascript"></script>
<script src="libs/jQuery/jquery.form.js" language="javascript" type="text/javascript"></script>
<script>
if (typeof jsCategory == 'undefined') {
    var objCategory = {
        addCate: function() {
            var src = "index.php?json=1";
            //alert(src);
            $.ajax({
                type: "POST",
                  url: src,
                //dataType: 'JSON',
                data: $('#fmAddCate').serialize(),
                success: function(xmlhttp){
                    var objData = xmlhttp.parseJSON();
                    if ((parseInt(objData.intIsOk) > 0) || (objData.intIsOk == true)) {
                        alert("Thêm mới thành công");
                    } else {
                        alert(objData.aryError);
                    }
                    $('#fmAddCate').unbind('button');
                },
                error: alert("Loi gi day"),
            });
        }
/*
        addCate: function() {
            //alert("Thêm mới thành công");
            var src = "?json=1";
            //alert(src);
            var options = {
                success:function(responseText, status){
                    if ((parseInt(responseText.intIsOk) > 0) || (responseText.intIsOk == true)) {
                        alert("Thêm mới thành công");
                    } else {
                        alert(responseText.aryError);
                    }
                    $('#fmAddCate').unbind('submit');
                },
                error: alert("Loi gi day"),
                url:       src,
                type:      'POST',
                dataType:  'json'
            };
            $('#fmAddCate').ajaxForm(options);
        }
*/
    };
}
</script>

<?php
$json = @$_GET['json'];
if ($json == 1) {
    $ary = array();
    $ary['intIsOk'] = 0;
    $ary['aryError'] = "Gặp lỗi ở đây";
    echo json_encode($ary);
    exit();
}
?>



<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<div new categories</div>
<div style="display:block; border-top:dotted 1px"></div>


<form name="fmAddCate" id="fmAddCate" action="" method="post" enctype="multipart/form-data">
    <div  style="float:left; width:100%">
        <input type="text" name="txtName" id="txtName" value=''/>
        <div>
            <div style="padding-left:20%; width:100%; padding-bottom:20px">
                <input type="button" value="Add" name="Add" onclick="objCategory.addCate()"/>
                <input type="reset" value="Reset"/>
            </div>       
        </div>
    </div>
</form>
prô php giúp với :ym_sad:
thank