Routing Error

[MuhammadWaqar_ul_islam]

i m  having error when i used routing example
<esri:RouteTask x:Name="MyRouteTask"
                            Url="http://gissrv7/ArcGIS/rest/services/Nadia_files/Karachi_NetworkAnalyst_visible/NAServer/Route"  
                SolveCompleted="MyRouteTask_SolveCompleted"
                            Failed="MyRouteTask_Failed" />

snap shot is attach

i dont why error apperas