Dovecot 2.4.0 fails to start with exit code 89

I've been trying to upgrade to 2.4.0. I've gone through the conf files, changing variables per the upgrade instructions. When I try to run sudo systemctl start dovecot.service, I get error 89. Journalctl shows me the error in question is "File name too long." I think it's coming from where 10-ssl.conf looks for the certs, but I'm probably wrong. Can anyone make a suggestion?

Ken