用c#连接统一错误的Mongodb

using UnityEngine;
using System; 
using System.Collections;
using System.Collections.Generic;
using MongoDB.Bson;
using MongoDB.Driver;
using MongoDB.Driver.Builders;  
using MongoDB.Driver.GridFS;  
using MongoDB.Driver.Linq;  
public class DBHandler : MonoBehaviour {
    string connectionString = "mongodb://localhost:27017";
    void Start () {
        /*
     * Establish connection
     */
        var client = new MongoClient(connectionString);
        var server = client.GetServer(); 
        var database = server.GetDatabase("unity");
        var shopcollections= database.GetCollection<BsonDocument>("vrshop");
        Debug.Log ("Connected!!0.0");
        //print all collections
        foreach (var document in shopcollections.FindAll()) {
            Debug.Log ("Get all info: 'n" + document);
        }
    }
}

这些代码用于工作，它可以成功地连接到mongodb，然而，今天，当我试图连接它时，它出现了一个错误:

MongoConnectionException: Unable to resolve host name 'localhost'.
MongoDB.Driver.MongoServerAddress.ToIPEndPoint (AddressFamily addressFamily)
MongoDB.Driver.MongoServerInstance.GetIPEndPoint ()
MongoDB.Driver.Internal.MongoConnection.Open ()
MongoDB.Driver.Internal.MongoConnection.GetNetworkStream ()
MongoDB.Driver.Internal.MongoConnection.SendMessage (MongoDB.Bson.IO.BsonBuffer buffer, Int32 requestId)
Rethrow as MongoConnectionException: Unable to connect to server localhost:27017: Unable to resolve host name 'localhost'..
MongoDB.Driver.Internal.DirectMongoServerProxy.Connect (TimeSpan timeout, MongoDB.Driver.ReadPreference readPreference)
MongoDB.Driver.Internal.DirectMongoServerProxy.ChooseServerInstance (MongoDB.Driver.ReadPreference readPreference)
MongoDB.Driver.MongoServer.AcquireConnection (MongoDB.Driver.ReadPreference readPreference)
MongoDB.Driver.MongoCursor`1+MongoCursorConnectionProvider[MongoDB.Bson.BsonDocument].AcquireConnection ()
MongoDB.Driver.Operations.QueryOperation`1[MongoDB.Bson.BsonDocument].GetFirstBatch (IConnectionProvider connectionProvider)
MongoDB.Driver.Operations.QueryOperation`1[MongoDB.Bson.BsonDocument].Execute (IConnectionProvider connectionProvider)
MongoDB.Driver.MongoCursor`1[MongoDB.Bson.BsonDocument].GetEnumerator ()
DBHandler.Start () (at Assets/DBHandler.cs:24)

我确信我使用相同的mongodb....怎么了?