or
sudo service airtime-liquisoap stop
then
sudo service airtime-liquisoap start

cheers

@Hoerich

$ sudo service airtime-liquidsoap stop
* Stopping Liquidsoap without notifying Monit process watchdog. If Monit is
* running it will automatically bring the Liquidsoap back up. You probably want
* 'stop-with-monit' instead of 'stop'.
Stopping Liquidsoap Playout Engine: ('Error loading config file: %s', error(111, 'Connection refused'))
Done.

$ sudo service airtime-liquidsoap start
* Starting Liquidsoap Playout Engine without Monit process watchdog. To make sure Monit is watching
* Liquidsoap, use 'start-with-monit' instead of 'start'.
Starting Liquidsoap Playout Engine: Unable to connect to the Airtime server.
<urlopen error [Errno 111] Connection refused>
traceback: Traceback (most recent call last):
  File "generate_liquidsoap_cfg.py", line 37, in <module>
    ss = ac.get_stream_setting()
  File "/usr/lib/airtime/api_clients/api_client.py", line 414, in get_stream_setting
    return self.services.get_stream_setting()
  File "/usr/lib/airtime/api_clients/api_client.py", line 137, in __call__
    f = urllib2.urlopen(req)
  File "/usr/lib/python2.7/urllib2.py", line 126, in urlopen
    return _opener.open(url, data, timeout)
  File "/usr/lib/python2.7/urllib2.py", line 400, in open
    response = self._open(req, data)
  File "/usr/lib/python2.7/urllib2.py", line 418, in _open
    '_open', req)
  File "/usr/lib/python2.7/urllib2.py", line 378, in _call_chain
    result = func(*args)
  File "/usr/lib/python2.7/urllib2.py", line 1207, in http_open
    return self.do_open(httplib.HTTPConnection, req)
  File "/usr/lib/python2.7/urllib2.py", line 1177, in do_open
    raise URLError(err)
URLError: <urlopen error [Errno 111] Connection refused>

Done.

Since my first post, I rebuilt liquidsoap with aac+ and opus and also applied 2.4.1 .  So the post at http://forum.sourcefabric.org/discussion/15123/upgrade-to-2-3-0-on-precise-fails is no longer my solution.

I followed https://wiki.sourcefabric.org/display/CC/Building+Liquidsoap+from+Source to compile liquidsoap.

./liquidsoap 'output.icecast(%mp3, mount="test.mp3", sine(), password="xxxx")' gets me a nice tone on my icecast server but airtime-liquidsoap will not start due to this error.

Any ideas?

Ok.  It's fixed.  As per other posts, this error means that airtime can't connect to Apache to do it's API stuff.

Once I figured that out I had to solve why. 

I did sudo dpkg-reconfigure airtime and sudo apt-get --reinstall airtime.  Neither of these fixed it.

I then tried the FQDN in /etc/apache2/sites-enabled/airtime-vhost and also played with /etc/hosts because I noticed it was resolving ::1 to localhost and apache didn't like the ipv6.  Removing localhost from the ipv6 section broke more.  In the end I have localhost in airtime-vhost and

127.0.0.1       localhost               localhost.twr.pri  #this line had been the FQDN before.
127.0.1.1       Mediashout.twr.pri      Mediashout

10.10.10.131    Mediashout.twr.pri      Mediashout
10.10.10.130    Mediastation.twr.pri    Mediastation

# The following lines are desirable for IPv6 capable hosts
::1     localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

After changing these, rebooting and running sudo apt-get --reinstall airtime it was working.  I just had to restart airtime-media-monitor and it was all good with AAC+ included!  :)