A recent update to Plesk ProFTPd package version 1.3.6-8.el6.art left ftp connectivity broken on a Plesk Panels 11.5.3 on CentOS 6.5 server. The update appended the following line to the tail of the /etc/proftpd.conf config file:

Include /etc/proftpd.d/*.conf

However, on the problematic server, the /etc/proftpd.d/ directory did not exist. The log file /var/log/messages was showing the following errors when attempting to start the xinetd service that runs ProFTPd.

Sep 8 11:30:54 triton xinetd[5803]: START: ftp pid=6085 from=::1
Sep 8 11:30:54 triton proftpd[6085]: error: cannot read configuration path ‘/etc/proftpd.d’: Not a directory
Sep 8 11:30:54 triton proftpd[6085]: fatal: Include: error including ‘/etc/proftpd.d/*.conf’: Invalid argument on line 95 of ‘/etc/proftpd.conf’
Sep 8 11:30:54 triton xinetd[5803]: EXIT: ftp status=1 pid=6085 duration=0(sec)

The simple solution is to comment the line out in the config file or create the /etc/proftpd.d/ directory.