c# - ArgumentException when adding many coordinates on the map -

i add pushpins can clickable on map. first, display them when add them on map, argumentexception occured , application crashes. if add 1 place on map, works when i'm trying add more places, crashes. whole list has been traversed.

my code:

var mycircle = new ellipse                 {                     fill = new solidcolorbrush(colors.blue),                     height = 20,                     width = 20,                     opacity = 50                 }; maplayer locationlayer = new maplayer(); foreach (var place in r.result)                 {                     //it's method created placecoordinate in format because can commas                     var placecoordinate = geolocalisation.getcoordinateingoodformat(place.google_lat,                                                                                     place.google_lng);                     if (placecoordinate == null)                     {                         continue;                     }                      var locationoverlay = new mapoverlay                         {                             content = mycircle,                             positionorigin = new point(0.5, 0.5),                             geocoordinate = placecoordinate                         };                      debug.writeline(place.title + ", lat: " + place.google_lat + ", long: " + place.google_lng);                     //display e.g.: soleil du midi, lat: 50.8382836, long: 4.3975321                      locationlayer.add(locationoverlay);  } mapcontrol.layers.add(locationlayer); //my map in xaml 

the error :

an exception of type 'system.argumentexception' occurred in system.windows.ni.dll , wasn't handled before managed/native boundary 

i have tried creating new instance of circle every point on map because can't add same uielement (in case circle) visual tree twice.

      var locationoverlay = new mapoverlay             {                     content = new ellipse()                             {                                     fill = new solidcolorbrush(colors.blue),                                     height = 20,                                     width = 20,                                     opacity = 50                             },                     positionorigin = new point(0.5, 0.5),                     geocoordinate = placecoordinate             };