I had this problem on a heavy forwarder taking things in with syslog-ng. Very simple test setup at this point only a couple files. My outputs.conf looked like the one in the original post except I was using hostnames not IP's. Turns out DNS was not resolving correctly, needed the FQDN or a DNS Search Path and it started working. I'm assuming this particular error message may be a catch-all for general communication problems. ... View more