I got CS0738 when class impelments an interface, and interface has a method, with return type interface.

And in class return type is a struct that implements return type interface.

Simply, this code shows the problem:

```cs
public interface IGame
{
    IPlayer WhoWin();
}

public interface IPlayer
{
    int ID { get; }
}

```

And in class:

```cs
public class MyGame : IGame
{
    // ERROR CS0738
    public MyPlayer WhoWin()
    {
        // ...
        return null;
    }
}

public class MyPlayer : IPlayer
{
    public int ID 
    {
        get
        {
            return ColorTranslator.ToWin32(Color);
        }
    }
    public Color Color;
}

```

What should I do? How can I solve the problem?