The original Lopster was locked out of the WPN ages ago with the implementation of WinMX 3 series any clients you come across will be acting purely as Open Nap clients, and so there should be no problem , that said some servers dont like WinMX users connecting to them.
You can change the client type in the Open Nap setting area by right clicking on a server address and then selecting
edit , try selecting another type of client (non WinMX ) to identify yourself to the server and see what happens, that should be interessting