Peer tries to roll back protocol version to 17.0, Error while processing ID

[greyghost509]

I have upgraded/reinstalled one of my tinc instances. Unfortunately, it appears that other machines cannot connect to it anymore although (to my best knowledge) I kept the configuration.

On the machines that try to connect to the upgraded machine (both running 1.1pre18), I get the following error messages:

Apr 17 11:05:18 tinc.l15[27046]: Peer l15_firefly12 (10.117.15.243 port 40893) tries to roll back protocol version to 17.0
Apr 17 11:05:18 tinc.l15[27046]: Error while processing ID from l15_firefly12 (10.117.15.243 port 40893)

I have checked that the keys are correct (so they should not cause an ID error). Any idea what is causing the problem here?