Unity 4.6 C#:类型或命名空间名称`IOS'；命名空间`GooglePlayGames'；中不存在

我有一款为iOS和android开发的游戏，这是突然开始出现错误的代码"Assets/GooglePlayGames/Platforms/PlayGamesClientFactory.cs（31,40）：error CS0234:类型或命名空间名称IOS' does not exist in the namespace GooglePlayGames"。你缺少程序集引用吗？"

这是代码：

using System;
using UnityEngine;
using UnityEngine.SocialPlatforms;
using GooglePlayGames.BasicApi;
namespace GooglePlayGames {
internal class PlayGamesClientFactory {
    internal static IPlayGamesClient GetPlatformPlayGamesClient() {
        if (Application.isEditor) {
            return new GooglePlayGames.BasicApi.DummyClient();
        }
#if UNITY_ANDROID
        return new GooglePlayGames.Android.AndroidClient();
#elif UNITY_IPHONE
        return new GooglePlayGames.IOS.IOSClient();
#else
        return new GooglePlayGames.BasicApi.DummyClient();
#endif
    }
}
}

错误在线：

return new GooglePlayGames.IOS.IOSClient();