I’m using Ubuntu 12.04. The X11 forwarding is enabled in /etc/ssh/sshd_config (X11Forwarding yes).
As I stared more verbose mode:
ssh -vvv -X remotehost
I received following error:
X11 forwarding request failed on channel 0
The solution is to add following to configuration file /etc/ssh/sshd_config:
Do not forget to restart ssh daemon:
service ssh restart