Simulator, XML-RPC error

I have noticed that when it fails to call an XML-RPC server after some tries, it just gives up and keeps going. Do you need a license to install your URCap? The ones that we have at our robots don’t need one. But I have noticed from other users that URCaps that launch an XML-RPC server might encounter issues on the URSim environment, like the example of MyDaemonSwing.