รบกวนขอคำแนะนำด้วยครับ jQuery + PHP upload ไฟล์ไม่ได้

<form class="form-horizontal" id="quotation_attach" method="post" enctype="multipart/form-data">

<div class="control-group ">
<label class="control-label">Title</label>
<div class="controls">
<input class="span6 m-wrap" id="AttachName" name="AttachName" type="text" required/>
</div>
</div>

<div class="control-group">
<label class="control-label">Attach File</label>
<div class="controls">
<div class="fileupload fileupload-new" data-provides="fileupload">
<div class="input-append">
<div class="uneditable-input">
<i class="icon-file fileupload-exists"></i> 
<span class="fileupload-preview"></span>
</div>
<span class="btn btn-file">
<span class="fileupload-new">Select file</span>
<span class="fileupload-exists">Change</span>
<input type="file" class="default" name="AttachFile" id="AttachFile" required="required"/>
</span>
<a href="#" class="btn fileupload-exists" data-dismiss="fileupload">Remove</a>
</div>
</div>
<span class="label label-important">NOTE!</span>
<span>File type must be .pdf file only.</span>
</div>
</div>

<div class="control-group">
<label class="control-label">Remark</label>
<div class="controls">
<textarea class="m-wrap span6" rows="3" id="AttachRemark" name="AttachRemark"></textarea>
</div>
</div>

<div class="form-actions">
<button type="submit" class="btn blue" name="btn-save" id="btn-save">Submit</button>
</div>

</form>

	$(document).on('submit', '#quotation_attach', function() {
	   $("#btn-save").html('loading ... &nbsp; <img src="../../assets/img/loader.gif" />').attr("disabled", true);
	   $.ajax({
		url: "process.php",
		type: "POST",
		data:  new FormData(this),
		contentType: false,
		cache: false,
		processData:false,
        success: function(data){
			 $("#msg-alert").fadeOut();
			 $("#msg-alert").fadeIn('slow', function(){
				 $("#msg-alert").html(data);
				 $("#process_modal").modal("show");
				 $("#btn-save").html('<i class="icon-save"></i>&nbsp;Submit').attr("disabled", false);	
			  });
		}
		 });   
	     return false;
    });

if(isset($_FILES["AttachFile"])){
	$temp = explode(".",$_FILES["AttachFile"]["tmp_name"]);
	$AttachFile = base64_decode($_POST['QuotRef']).'_'.md5(date("U")).'.'.end($temp);
	$file_dir = "attachment/".$AttachFile;
		
	$data = array();
	$data["attach_name"] = mysqli_real_escape_string($conn, $_POST['AttachName']);
	$data["attach_file"] = $AttachFile;
	$data["attach_remark"] = mysqli_real_escape_string($conn, $_POST['AttachRemark']);
	$data["last_modify"] = $last_modify_user;

    if(move_uploaded_file($_FILES["AttachFile"]["tmp_name"],$file_dir)){	
	$insert_attach = insert_data("tbl_attach",$data);	
	}
			if($insert_attach)
			{
				echo $alert_complete;
			}
			else{
				echo $alert_error;
			}
	}