How to Fix xvncviewer: unable to open display "" vncviewer: unable to open display ""

Fix
====
Use -X instead od -x

#ssh -X saju@192.168.56.102

Error
====
saju@ubuntu:~$ xvncviewer :0

VNC Viewer Free Edition 4.1.1 for X - built Jan 14 2013 22:25:00
Copyright (C) 2002-2005 RealVNC Ltd.
See http://www.realvnc.com for information on VNC.
xvncviewer: unable to open display ""
saju@ubuntu:~$


saju@ubuntu:~$ vncviewer :0

VNC Viewer Free Edition 4.1.1 for X - built Jan 14 2013 22:25:00
Copyright (C) 2002-2005 RealVNC Ltd.
See http://www.realvnc.com for information on VNC.
vncviewer: unable to open display ""
saju@ubuntu:~$