Xvnc inetd solution stopped working

We have been using a Xvnc server system in XDMCP mode to present a login dialog to the VNC viewer, so that the user can log in as from a local screen.
This has been working fine until recently, I suspect the recent tightening of security has changed the conditions.
We suddenly got a black screen instead of the greeter.
We tried to reinstall from scratch using the same methods as when we started, and now we caot even get a black screen.

OS: Ubuntu 14.04 LTS xfce4
openbsd_inetd
Xvnc server:TurboVNC Xvnc -inetd mode

/etc/services
....
# Local services
vnc 5950/tcp

/etc/inetd.conf
vnc stream tcp nowait nobody /opt/TurboVNC/bin/Xvnc Xvnc -inetd -query localhost -once -geometry 2560x1024 -depth 24

/etc/lightdm/lightdm.conf
...
[XDMCPServer]
enabled=true

This combination used to work fine, but now TurboVNC viewer responds for coection "vnchost":50 with "Coection closed".
Testing with telnet:
telnet localhost 5950
Trying ::1...
Trying 127.0.0.1...
Coected to localhost.
Escape character is '^]'.
RFB 003.008
Coection closed by foreign host.

So it seems like some security issue.
Any constructive input is appreciated.

BN

Note: In this post, my system is NOT Ubuntu studio, as is shown in my profile.