急：请教Ext3.3 Chart数据有返回，图形无法显示

[jessonmiao]

var chartstore = new Ext.data.JsonStore({
url:'/commonbasedata/itemProperties.do?method=showChart',
root:'chartview',
fields:[
{name:'name',type:'string'},
{name:'value',type:'int'}
]
});
Ext.chart.Chart.CHART_URL = '../../images/resources/charts.swf';

var chart = new Ext.Panel({
height:400,
layout:'fit',

items:{
xtype: 'linechart',
store: chartstore,
xField: 'name',
series:[{
type:'line',
displayName:'Main Plan',
yField:'value'
}]
}
});

后台返回的JSON
{"chartview":[{"name":"bucket1","value":"0"},{"name":"bucket2","value":"28"},{"name":"bucket3","value":"7"},{"name":"bucket4","value":"7"},{"name":"bucket5","value":"7"},{"name":"bucket6","value":"6"},{"name":"bucket7","value":"7"},{"name":"bucket8","value":"7"},{"name":"bucket9","value":"7"},{"name":"bucket10","value":"6"},{"name":"bucket11","value":"7"},{"name":"bucket12","value":"7"},{"name":"bucket13","value":"7"},{"name":"bucket14","value":"7"}]}

用FF看了，有响应，也有JSON返回，为什么就是显示不出图。
有没有高手知道原因，坐等解答！！！

[jessonmiao]

难道就没有高手能指点下吗？