ubuntu 14.04 x2go install error "Authentification Failed The host key for this server was not found but an othertype of key exists.An Attacker might change" / blanc&black screen problem

Server installation ( ubuntu server 14.04.1)
http://wiki.x2go.org/doku.php/doc%3ainstallation%3ax2goserver
http://www.howtoforge.com/how-to-install-x2goserver-on-ubuntu-14.04-as-vnc-alternative

# sudo apt-get install python-software-common(14.0 only)

sudo add-apt-repository ppa:x2go/stable
sudo apt-get update
sudo apt-get install x2goserver x2goserver-xsession

Client installation (ubuntu desktop 12.04)
https://lbtwiki.cern.ch/bin/view/Main/InstallingX2go

ubuntu-software-center x2go
or
sudo apt-get install x2goclient

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Poblem of "Authentification Failed The host key for this server was not found but an othertype of key exists.An Attacker might change"
http://john.wesorick.com/2011/11/issues-installing-x2go.html

This will happen if you SSH into the server before installing x2go. SSH by default likes ecdsa keys, and x2go doesn't. On the server, edit the ssh config:

$sudo nano /etc/ssh/sshd_config

Then comment out this line with a #:

HostKey /etc/ssh/ssh_host_ecdsa_key

Now restart ssh:

$sudo service ssh restart

On your client you need to remove your old key. I just removed all of them.

$rm .ssh/known_hosts

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Blank/black screen after longin when xfce = xface desktop seesion did not start

The session type XFCE is not available: set xfce4-session (on ubuntu-desktop 12.04.5)
x2go session preference>session type >(choose) custom session > xfce4-session (in "Command")