ext js表单提交的有关问题

ext js表单提交的问题

 function Add() {

            if(app.stuForm.form.isValid())

            {

                Ext.MessageBox.show({

                title: '请稍候',

                msg: '数据提交中...',

                progressText: '',

                width: 300,

                progress: true,

                waitConfig:{interval:600},//0.6s进度条自动加载一定长度  

                closable:true, 

                wait:true, 

                animEl: '数据处理中......'

                fn:doAction });

                setTimeout(function(){Ext.MessageBox.hide()},5000);

                app.stuForm.form.doAction('submit',{

                    url: '../Commen/UploadFile.aspx?Opt=addstudent',

                    method:'post',params:'',

                    success:function(form,action){

                        var strSuccess = action.result.success.trim();

                        if(strSuccess == "true")

                        {

                            Ext.Msg.alert('系统提示','   添加成功   ');                            

                        }

                        else

                        {

                            Ext.Msg.alert('系统提示',"   " + action.result.msg+"   " );

                        } 

                    },

                    failure:function(){ 

                        Ext.Msg.alert('系统提示','添加失败,连接服务器失败');

                    }                

                });

            }

	    }

提交了这个之后，执行了后台，且后台返回了response.write(success:true),这个是神马状况，为什么不能执行sucess或者failure,难道是后台的数据，前台没有接受到后台返回的东西？求解释。
------解决思路----------------------
你确定后台已经传回数据到前台了?
firebug看一下