Command find failed: Failed to parse: { find: "bar", filter: {}, skip: 0, readPreference: { mode: "secondaryPreferred", tags: [ { dc: "ny", rack: "1" }, { dc: "sf" } ] }, noCursorTimeout: false, allowPartialResults: false }. Unrecognized field 'readPreference'..

var tagSets = new TagSet[]
{
    new TagSet(new [] { new Tag("dc", "ny"), new Tag("rack", "1") }),
    new TagSet(new [] { new Tag("dc", "sf") })
};

MongoClientSettings clientSettings = new MongoClientSettings
{
    Server = new MongoServerAddress("server"),
    ReadPreference = ReadPreference.SecondaryPreferred.With(tagSets)   <---- Exception
    //ReadPreference = ReadPreference.SecondaryPreferred   <----- Working
};

MongoClient client = new MongoClient(clientSettings);
MongoServer server = client.GetServer();
MongoDatabase database = server.GetDatabase("foo");
MongoCollection<BsonDocument> collection = database.GetCollection<BsonDocument>("bar");

MongoCursor<BsonDocument> cursor = collection.FindAll();

foreach (BsonDocument bsonDocument in cursor)
{
    Console.WriteLine(bsonDocument.ToString());
}