I even struggled around with a lot of bugs on Ubuntu+XEN and then had to switch to Debian7. On Linux use OpenXenManager as alternative working fine (internally using something like vncviewer).
For Windows Users:
Use SSH+Tunneling ports (5901 increasing for each running VM-Instance) as TCP-Tunnel over SSH. Keep in mind to disconnect the Citrix XenCenter remote connection to your XEN-Instance in case you are using it with XCP-XAPI. Else the VNC ist locked by XEN Central!
Same problem for me!
I even struggled around with a lot of bugs on Ubuntu+XEN and then had to switch to Debian7. On Linux use OpenXenManager as alternative working fine (internally using something like vncviewer).
For Windows Users:
Use SSH+Tunneling ports (5901 increasing for each running VM-Instance) as TCP-Tunnel over SSH. Keep in mind to disconnect the Citrix XenCenter remote connection to your XEN-Instance in case you are using it with XCP-XAPI. Else the VNC ist locked by XEN Central!
Use f.e. UltraVNC as RDP-Client.