Hi @DonalC, hm, have you tried looking at
sudo journalctl -u NetworkManager -f
and trying to connect? Anything occur there?
This error sounds similar to what I observed here (specifically, see the links). You can try to reduce the security in the local-access-point by changing the configuration setting proto from rsn to wpa under [local_access_point], and rebooting the machine. (Caution: this might cause the clients to disconnect, and you may need to reconnect them) (Second caution: some computers will warn you about connect to an unsecure WPA network, you can ignore this).