I am using v2.0
To solve the problem I had to add this line
ESRI.ArcGIS.Client.Geometry.MapPoint webmercatorP = ESRI.ArcGIS.Client.Bing.Transform.GeographicToWebMercator(new ESRI.ArcGIS.Client.Geometry.MapPoint(0, 0));
But it doesn't make any sense. With this line the solution works fine