var collection = database.GetCollection("testconnection");
dynamic p = new MongoDB.Bson.ObjectModel.BsonDynamicDocument();

p.Id = Guid.NewGuid();
collection.Insert(p);
var value = (Guid)p.Id;
var item2 = collection.AsQueryable().Where(item => item.GetValue("Id") == value).FirstOrDefault();

this is giving an error.

I have attached a sample project and you can see it there.