Hello and welcome to the forums.
Comment out ...and make sure there is no space between "start" and "xfce4" in your last line. Like this:
If that doesn't work, there is a log file in your ~/.vnc folder that might help identify the problem.
# Uncomment the following two lines for normal desktop:
# unset SESSION_MANAGER
# exec /etc/X11/xinit/xinitrc
[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
xsetroot -solid grey
vncconfig -iconic &
x-terminal-emulator -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &