It looks like the 3D and special effects play havoc with the VNC server - not displaying properly, etc.
gdmsetup- the 'login settings' manager under the administration menu, or go to the top-right switch icon and and click System Settings, then 'Login Screen'.
Enter your admin password, then select 'Ubuntu Classic (No effects)' as the default session. Reboot or logout/login.
This changes ubuntu to use the standard gnome menubar and disables the 3d and animation effects.
I found that VNC worked much better with the classic menu and desktop effects off :-).