Sometimes connecting to the collectd unixsocket is not possible giving a connection refused.
This can be fixed manually by removing manually the socket file
and then restart collectd
collectd does not create a new socket file when there is already such a file. But the old file, which is not connected to any process certainly refuses connections all the time. Probably it is enough to remove that file if it exists whenever collectd will be started.
This is easily reproduceable:
killall -9 collectd /etc/init.d/collectd restart
not accepting anymore