arcgis flex api queryTask keep loading

In my flash builder mxml file, I load a datagrid with data get from database through web service. In the datagrid I create a context menu "select and zoom" to select and zoom to a feature (attribute value from the datagrid selected row), but when I select a row, and call this "select and zoom" function, the busy cursor will always there.

From the map service page, I can successfully query the same feature as follows:

I can also confirm that the selected feature exist and loaded, but the situation is when I call the select function on datagrid selected row, it keep loading.

I am stuck at the problem for quite a long time but still cannot figure out what is wrong.

Don't know whether it is code issue or setting issue, my mxml code is listed below:

<viewer:BaseWidget xmlns:fx="http://ift.tt/rYUnH9"
               xmlns:s="library://ns.adobe.com/flex/spark"
               xmlns:mx="library://ns.adobe.com/flex/mx"
               xmlns:viewer="com.esri.viewer.*"
               xmlns:esri="http://ift.tt/1tsyegi"
               right="420" bottom="220" width="850" height="449" layout="absolute"
               widgetConfigLoaded="init()">
<fx:Script>
    <![CDATA[
        import com.esri.ags.FeatureSet;
        import com.esri.ags.Graphic;
        import com.esri.ags.geometry.Extent;
        import com.esri.ags.geometry.Polyline;
        import com.esri.ags.layers.GraphicsLayer;
        import com.esri.ags.tasks.QueryTask;
        import com.esri.ags.tasks.supportClasses.Query;
        import com.esri.ags.layers.FeatureLayer;

        import mx.collections.ArrayCollection;
        import mx.controls.Alert;
        import mx.rpc.AsyncResponder;
        import mx.rpc.events.FaultEvent;
        import mx.rpc.events.ResultEvent; 
        import mx.utils.StringUtil;


        private var graphicsLayer:GraphicsLayer;
        private var hashmapOfExistingGraphics:Object = new Object();

        public function init():void {

            graphicsLayer = new GraphicsLayer();
            graphicsLayer.symbol = sfs;
            map.addLayer(graphicsLayer);
            ws.GetLoc(); 

            var cm:ContextMenu = new ContextMenu();
            cm.hideBuiltInItems();
            var item:ContextMenuItem = new ContextMenuItem("Select and Zoom");
                    item.addEventListener(ContextMenuEvent.MENU_ITEM_SELECT, onSelectItem); 
            cm.customItems.push(item);
            datagrid.contextMenu = cm;          
        }

        private function onSelectItem(e:ContextMenuEvent):void{
            //event.contextMenuOwner
            if(datagrid.selectedIndex >= 0){        
                this.cursorManager.setBusyCursor();
                var query:Query = new Query;
                query.where = "SELECT * from dev_db.DBO.BQ_Segment_1 WHERE BQ_no_ = '" + datagrid.selectedItem.bqNo + "' and Segment_ID = '" + datagrid.selectedItem.segmentID + "'";   
                queryTask.execute(query, new AsyncResponder(onResult, onFault));  

                function onResult(featureSet:FeatureSet, token:Object = null):void  
                {  
                    graphicsLayer.clear();  
                    if (featureSet.features.length == 0)  
                    {  
                        Alert.show("No feature found. Please try again.");
                    }  
                    else  
                    {  
                        Alert.show("feature exist....");
                        var unionExtent:Extent;  
                        var myFirstGraphic:Graphic = featureSet.features[0];  

                        unionExtent = Polyline(myFirstGraphic.geometry).extent;  // problem line

                        for each (var myGraphic1:Graphic in featureSet.features)  
                        {  
                            graphicsLayer.add(myGraphic1);  
                            unionExtent = unionExtent.union(Polyline(myGraphic1.geometry).extent);  
                        }  
                        map.extent = unionExtent;  
                    }  
                }   

                function onFault(info:Object, token:Object = null):void  
                {  
                    Alert.show(info.toString());  
                }  
            }else{
                Alert.show("Select a record first","ATTENTION");
            }
        }



        public function GetLoc(event:ResultEvent):void {
            // Databind data from webservice to datagrid
            datagrid.dataProvider = event.result; 
        }

        public function fault(event:FaultEvent):void {
            // Oppps some error occured
            Alert.show(event.toString());
        }       
    ]]>
</fx:Script>
<fx:Declarations>
    <mx:WebService id="ws" wsdl="http://localhost/TestWebService/Service.asmx?WSDL" fault="fault(event)">
        <mx:operation 
            name="GetLoc" 
            resultFormat="object"
            result="GetLoc(event)"
            />
    </mx:WebService>
    <esri:SimpleFillSymbol id="sfs" alpha="0.7" color="0xFF0000"/>          
    <esri:QueryTask id="queryTask"
                    showBusyCursor="true"
                    url="http://localhost:6080/arcgis/rest/services/MyService/MapServer/1"
                    useAMF="false"/>

    <esri:PictureMarkerSymbol id="sps"/>

</fx:Declarations>

<viewer:WidgetTemplate id="wTemplate" x="0" y="2" width="834.5" height="447"
                       textDecoration="none">
    <viewer:layout>
        <s:BasicLayout/>
    </viewer:layout>
    <s:HGroup x="44" y="10" width="757" height="350">

        <s:DataGrid id="datagrid" width="732" height="329">
            <s:columns>
                <s:ArrayList>
                    <s:GridColumn headerText="BQ No" dataField="bqNo"/>
                    <s:GridColumn headerText="BQ Segment" dataField="bqSegment"/>
                    <s:GridColumn headerText="Contract No" dataField="contractNo"/>
                    <s:GridColumn headerText="Project Title" dataField="projectTitle"/>
                    <s:GridColumn headerText="Completion Date" dataField="completionDate"/>
                    <s:GridColumn headerText="Drain Name" dataField="drainName"/>
                    <s:GridColumn headerText="Road Name" dataField="roadName"/>
                    <s:GridColumn headerText="Description" dataField="shape"/>
                </s:ArrayList>          
            </s:columns>
        </s:DataGrid>       
      </s:HGroup>

     </viewer:WidgetTemplate>     
    </viewer:BaseWidget>

I am using ArcGIS API for Flex 3.6.