Easy enough to tell if it's part of the module:

$ grep 'read command channel socket' $(perldoc -l Net::FTPSSL)
                             ? "Can't read command channel socket: $!"
[download]

As to handling it - the code around that line makes it relatively obvious why the message is being generated:

        # Now lets read the response from the command channel.
        my $read = sysread( $self, $data, 4096);
        unless( $read ) {
          # Not called as an object member in case $self not a FTPSSL 
+obj.
          _croak_or_return ($self, 0, (defined $read)
                                ? "Can't read command channel socket: 
+$!"
                                : "Unexpected EOF on command channel s
+ocket!");
          return (CMD_ERROR);
        }
     }
[download]

Combined with the debug log, it looks like you're losing your connection toward the end of the transaction. What happens if you try all of the above manually?

(I also find it rather strange that an automated interaction would invoke 'HELP'. Doesn't smell kosher to me; seems like there's some kind of odd problem happening. In any case, 'perl -d' is your friend.)

-- 
Education is not the filling of a pail, but the lighting of a fire.
 -- W. B. Yeats