NBS doesn't use any SSL settings, this is nothing to do with the NBS software. Any SSL cert should be on the server but this is not a requirement for NBS. To meet PCI compliance NBS is designed to never take any CC or bank details on the NBS server, only to accept this information on the banking server which should deal with it's own SSL security.
Unless there is something I'm missing, I can't see any reason paypal would need you to alter anything on your server to meet a IPN request for SSL. I suggest you get directly in touch with paypal and see if there is some kind of scam going around.
Unless there is something I'm missing, I can't see any reason paypal would need you to alter anything on your server to meet a IPN request for SSL. I suggest you get directly in touch with paypal and see if there is some kind of scam going around.