Exception stack trace is http://pastebin.com/DFAz5eE4
Sample code is
namespace ConsoleApplication
{
class Program
{
public class B
{
[BsonId]
public ObjectId Id

{ get; set; }
public int GetMe { get; set; }

public object[] Items

{ get; set; }

}
static void Main(string[] args)

{ var server = MongoServer.Create("mongodb://localhost/?safe=true"); var database = server["onlinetests"]; var bcoll = database.GetCollection<B>("btest2"); var bee = new B(); bee.GetMe = 1; bee.Items = new object[1]; bee.Items[0] = 123; bcoll.Insert(bee); var bsonValue = new BsonInt32(bee.GetMe); // throws on deserialization var test = bcoll.FindOne(MongoDB.Driver.Builders.Query.EQ("GetMe", bsonValue)); }

}
}