This code: class IP: BaseClass { ... private string GetBusinessID(Int64 id) { return Load<IP>(id).IPBusID; } ... } is incorrectly made static. ("Load" is a static method defined in BaseClass.) Resulting method: class IP: BaseClass { ... private static string GetBusinessID(IP ip, Int64 id) { return ip.Load(id).IPBusID; } ... } The "IP" parameter should not have been added in this case. I can upload a .sln for this if you want.