he VNC client bundled with Ubuntu, Vinagre, works half the time. Fortunately, we can also VNC with the installed “Terminal Server Client”
The “VNC” option with the default installation of Terminal Server Client is disabled or grayed-out.
To enable it you need to install the xtightvncviewer package in Synaptic or with the following command on the terminal
sudo apt-get install xtightvncviewer