getting Query error.

[SubhashSheladia]

Getting below error.....
[RPC Fault faultString="Unable to complete  operation." faultCode="400" faultDetail="Unable to complete Query operation."]


My Code is.....

var query:Query = new Query();
       query.outSpatialReference=myMap.spatialReference;
       query.outFields=["PERMIT_NBR","OBJECTID","ACCOUNT_NBR"];
       query.returnGeometry=true;      
       //query.text=txtCity.text;
       query.where="Name = '" + txtCity.text + "'";

      //CityQueryTask.execute(query,null);
     
      CityQueryTask.execute(query, new AsyncResponder(onResult, onFault));
      function onResult(featureSet:FeatureSet, token:Object = null ):void
      { 
       Alert.show("Hi");
       //querygraphic.graphicProvider = CityQueryTask.executeLastResult.features;
      }
      function onFault(info:Object, token:Object = null):void
      {
       Alert.show( info.toString() );
      }     

Please help me.

Thanks