MongoDB连接失败？

//使用AppSettings方式和配置文件连接，灵活控制MongoDb数据库位置string ConnectionString = ConfigurationManager.AppSettings["mongoDbConnection"];创建连接池,设定等待队列数,设定最大连接池MongoServerSettings mongoSetting = new MongoServerSettings();mongoSetting.MaxConnectionPoolSize = 15000;     //设定最大连接池mongoSetting.WaitQueueSize = 500;  //设定等待队列数mongoSetting.Server = new MongoServerAddress(ConnectionString, 27017);MongoServer mongodb = MongoServer.Create(mongoSetting); // 连接数据库MongoDatabase mongoDataBase = mongodb.GetDatabase("dmtmOSMcoinDB"); // 选择数据库名MongoCollection mongoCollection = mongoDataBase.GetCollection(fileTable); // 选择集合，相当于表mongodb.Connect();

报错：

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