How to enable XDMCP?

Hello everyone,
I installed AIX the other day (several times!) but I can't get XDMCP to work.
I remember from when I installed it the last time it worked out of the box.
So why doesn't it work now?
This is the error message I get:

XDMCP fatal error: Session failed Session 2 failed for display tuxbox:
1: Cannot open display

Is there anything I have to enable?
I googles a lot but didn't find any useable help.

Maybe I'm not understanding your problem. It looks like the AIX box does not have the privilege to run X on the tuxbox. If that is the case then entering "xhost +aixhostname" on tuxbox will need to be done.

Another thing to look at is try adding or uncommenting the line

:0 Local local@console /usr/lpp/X11/defaults/xserverrc -T -force :0

in /etc/dt/config/Xservers and then I had to reboot to get it going on the local graphical display. You may have a more elegant way.

I think xhost may be the problem. I added my RS/6000 on tuxbox (which worked) and also tried adding tuxbox on my rs6k, that didn't work:

On AIX, xhost doesn't even work:
# xhost +tuxbox
1356-200 xhost unable to open display ""
# xhost
1356-200 xhost unable to open display ""

I think that could be the problem. Any idea?

You would have to have an X session running on the AIX box for xhost + to work.
For example, when I ssh from my linux box to my AIX box and run xhost + I get the same error you get: 1356-200 xhost unable to open display ""

But when I login in to the AIX box via xdmcp, open a dtterm and enter "xhost +" I get the message "access control disabled, clients can connect from any host".

This means that xhost must be run from the machine with the display connection.