[slurm-users] error: unpack_header: protocol_version 9472 not supported

I have built Slurm 23.11.7 on two machines. Both are running Ubuntu 22.04. While Slurm runs fine on one machine, on the 2nd machine it does not. First machine is both a controller and a node while the 2nd machine is just a node. On both machines, I built the Slurm debian package as per the Slurm docs instructions. Slurmd logs show this:

error: unpack_header: protocol_version 9472 not supported error: unpacking header error: destroy_forward: no init error: slurm_receive_msg_and_forward: [[host-4.attlocal.net]:38960] failed: Message receive failure error: service_connection: slurm_receive_msg: Message receive failure debug: _service_connection: incomplete message