I'm on Raspberry pi 2, running Raspian, and using Ubuntu 14.04. I am using the tightvncserver. I don't think I should have to start a new 'X' desktop each time I want to VNC into the pi, but whenever I tried to vnc into the previously established :0 or :1 it told me that it was "closed" and refused to connect. This is after running:
vncserver :0 -geometry 1920x1080 -depth 24
I got it running by typing the same thing with a :2 and then vnc-ing in, but I think there's another way.