LinuxMusicians

Hello,
I'm trying to use guitarix in UbuntuStudio 16.04.2. When I start guitarix, there is a message displayed, that there is no JACK server running. I hit "Start JACK" and QJackCtl opens and starts a JACK server. The server starts without problems. But guitarix does not connect to it. Instead it sends an Error message "I really tried to get Jack up and running, Sorry".
When I start JACK via QJackCtl first and then start guitarix, the same happens. The problem also happens with other applications like Ardour and Pulseaudio. None of the applications appear in the connections window.
I know the JACK server is running, because I can connect the guitar input from my USB Audio Interface directly to the computers speakers and I can hear sound.
To me it seems, that the applications "can't see" the running JACK server. I tried to kill jackd and jackdbus several times, but it didn't change anything. Neither have I changed the server name (at least not on purpose).
Any advise would be appreciated. Thank you!

Thank you very much for your advise.
The server name as displayed by QJackCtl was still 'default'. It was the first usage of JACK after fresh install of UbuntuStudio.
But deleting the configuration files solved the problem. I also removed ~/.config/jack/conf.xml.
Now all the other applications appear in the connections window and everything seems to work.
Thanks again.