public class TestInfo
{
public string Id

{ get; set; }

public Object Items { get; set; }

}

TestInfo testInfo = new TestInfo();
testInfo.Id = ObjectId.GenerateNewId().ToString();
testInfo.Items = new List<string>()

{ "A", "B","C","D","E" }

;

collection.Save<TestInfo>(testInfo);

var item = collection.FindOneById(testInfo.Id);

Exception:

An error occurred while deserializing the Items property of class Test.Program+TestInfo: Cannot deserialize System.Object from BsonType Array.