New version 1.3.1 available which removes the broken alert system:
https://www.reddit.com/r/nyancoins/comments/78qykw/nyancoin_wallet_131_without_alert_messages/

This prevents the 'URGENT: Alert key compromised, upgrade required' message from being displayed.

The message can be ignored as it is totally meaningless, however it can be annoying particularly with the Windows client.