Thanks! That was the solution for me on ubuntu too. I believe this actually relates to a permissions problem when using VNC. So for any user who wants to do vnc'ing you'll need to (as root) do
Code:
adduser theusername tty
...and the users will need to kill their existing vncservers. Log in with a new SSH session (to pick up the new 'tty' group) and start new vncservers.