JQuery+Ajax+Ashx+Base64 data無法傳遞的問題

$.ajax({
               url:'/financepage/finance_public/ImgUpload.ashx',
               type:'POST',
               data:'Action=Base64Upload&Img='+content,
               //async:false,  //關閉異步
               dataType:'text',
               //contentType:"application/json; charset=utf-8",  //注釋掉后就可以傳遞data了
               beforeSend:function(){f_alert2("waitting","圖片正在上傳中...");},
               error:function(XMLHttpRequest, textStatus, errorThrown){
                    //alert(XMLHttpRequest+" , "+textStatus+" , "+errorThrown)
                    f_alert2("closeWaitting","");
                    f_alert2("error","上傳過程中出現意外錯誤");
               },
               success:function(result){
                    f_alert2("closeWaitting","");
                    if(result=="false"||result==undefined||result=="none"||result==""){
                        f_alert2("error","圖片上傳失敗");
                    }
                    else{
                        //alert(result);
                        parent.parent.document.getElementById(GetURLParam("hiddName").value=result);
                    }
               }
       });