Edit the/root/.vnc/xstartup file so it reads,

xrdb $HOME/.Xresources
xsetroot -solid grey
x-terminal-emulator -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &
gnome-session &

After doing this kill the vnc processes and restart. 

Note : You may need to change the last line if you are using KDE.