Package: x2goserver
Version: 4.0.1.19

I have a Linux Mint 18 x2go client and a Debian Testing x2go server. And I
update both at random intervals.
Things just worked for ages. I think I went from Linux Mint 15 to 18.
Debian is also really uptodate.

Then at one moment - I don't exactly know when because I don't use x2go
daily - I started getting this error message.

Connection failed. xset: unable to open display ""
http://i.imgur.com/Z6yQb4R.png

This sounds like one of those xorg errors you get when doing x stuff while
not logged into a virtual terminal, but in the case of x2go, I use the
magic but don't know how it works, so I have no idea where to start looking.

Client machine:
    Linux Mint 18 (AKA Ubuntu 16.04)
    x2goclient 4.0.5.1-1
    pyhoca-gui 0.5.0.4-1*
    pyhoca-cli 0.5.0.2-1*
Server:
    Debian Testing
    x2go-server 4.0.1.19-0x2go2+git20160621.1064+stretch.main.1
    x2goserver-xsession 4.0.1.19-0x2go2+git20160621.1064+stretch.main.1
    nxagent 2:3.5.0.32-0x2go1+git20160614.734+stretch.main.1

*) Never heard of there. I don't think I ever installed them. I figured I
didn't have them installed before so I installed them now. Didn't fix my
problem though.