问WCF异步CTP银灯

EN

[ServiceContract]
public interface iGame
{
    [OperationContract]
    Task<bool> Request ( string Key );
}

[ServiceBehavior ( InstanceContextMode = InstanceContextMode . Single , ConcurrencyMode = ConcurrencyMode . Multiple , UseSynchronizationContext = true )]
public class Game : iGame
{
    public async Task<bool> Request ( string Key )
    {
        return await Task . Factory . StartNew ( ( ) => true );
    }
}

    private async void myButton_Click ( object sender , RoutedEventArgs e )
    {
        if ( await Messenger . Instance . Client . Request ( XXX . Text ) ) // Exception
            NavigationService . Navigate ( new Uri ( "/Views/YYY.xaml" , UriKind . Relative ) );
    }

System.InvalidOperationException: The contract 'iGame' contains synchronous operations, which are not supported in Silverlight. Split the operations into "Begin" and "End" parts and set the AsyncPattern property on the OperationContractAttribute to 'true'. Note that you do not have to make the same change on the server.
   at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<ThrowAsync>b__0(Object state)