The solution:
as root, do the following two things :
1) edit /etc/sysconfig/vncservers
specify vncserver parameters for each vncserver that you want to start (at boot)

2) run /etc/init.d/vncserver start

voila, you're in business

(And then run system-config-services and make sure vncserver is checked to run at boot so you don't have to do the above every time)

a quick scan of /etc/init.d/vncserver just shows that it runs vncserver for the users specified with the parameters specified, so I don't know what the difference is between that and the user just running vncserver on the command line. But obviously there is something special that is done by the init.d script.

I'm able to run vncserver from the commandline as the user in FC4, ubuntu 6.06, debian, CentOS4, etc. First time I've had this particular issue.

I found this post to give me the clue:
http://www.realvnc.com/pipermail/vn...ber/052743.html

On the affected machine, xfce4 seems to run fine over the console (along with GNOME and KDE), but when I try to run xfce4 via vnc, things only seem to half work, if that. The panel and the window manager fail to run. If I try to manually start xfwm4 within an xterm, it segfaults and takes the xterm and taskbar with it! I don't have a menu. So, it's pretty much useless.

Again, these problems are just with vnc.  Choosing xfce4 with gdm and then logging in from the console works fine.  Xfce is a nice compromise between the heavy desktops (KDE,GNOME) and the ultralight window managers (fluxbox,flwm,twm, etc.) so I'm dissappointed, to say the least, that I can't run it via vnc.

Note that I am starting vnc via the command line (vncserver) not using xinetd/gdm to start vnc.

My system:
mobo,CPU,ram: ECS K7SOM+5c Duron950Mhz 384MB crucialPC100SDRAM
OS: FC5, kernel 2.6.15-1.2054_FC5

xfce4 rpms installed:
xfcalendar.i386 4.2.3-2.fc5 installed
xfce-mcs-manager.i386 4.2.3-2.fc5 installed
xfce-mcs-plugins.i386 4.2.3-3.fc5 installed
xfce-utils.i386 4.2.3-4.fc5 installed
xfce4-datetime-plugin.i386 0.3.1-7.fc5 installed
xfce4-diskperf-plugin.i386 1.5-6.fc5 installed
xfce4-fsguard-plugin.i386 0.2.1-4.fc5 installed
xfce4-icon-theme.noarch 4.2.3-2.fc5 installed
xfce4-iconbox.i386 4.2.3-3.fc5 installed
xfce4-mixer.i386 4.2.3-2.fc5 installed
xfce4-mount-plugin.i386 0.3.3-4.fc5 installed
xfce4-panel.i386 4.2.3-4.fc5 installed
xfce4-quicklauncher-plugin.i386 0.81-4.fc5 installed
xfce4-session.i386 4.2.3-3.fc5 installed
xfce4-session-engines.i386 4.2.3-3.fc5 installed
xfce4-showdesktop-plugin.i386 0.4.0-6.fc5 installed
xfce4-systemload-plugin.i386 0.3.6-6.fc5 installed
xfce4-systray.i386 4.2.3-2.fc5 installed
xfce4-taskbar-plugin.i386 0.2.2-6.fc5 installed
xfce4-windowlist-plugin.i386 0.1.0-6.fc5 installed
xfce4-xkb-plugin.i386 0.3.5-2.fc5 installed
xfdesktop.i386 4.2.3-4.fc5 installed
xffm.i386 4.2.3-4.fc5 installed
xfsprogs.i386 2.7.3-1.2.1 installed
xfwm4.i386 4.2.3.2-5.fc5 installed
xfwm4-themes.noarch 4.2.3-2.fc5 installed

vncserver rpms installed:
vnc.i386 4.1.1-39.fc5 installed
vnc-server.i386 4.1.1-39.fc5 installed

contents of ~/.vnc/xstartup
#!/bin/sh

# Uncomment the following two lines for normal desktop:
# unset SESSION_MANAGER
# exec /etc/X11/xinit/xinitrc

export VNCSESSION="TRUE"
[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
xsetroot -solid grey
vncconfig -iconic &
xterm -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &
startxfce4
#twm &

contents of
~/.vnc/localhost.localdomain:5.log
Xvnc Free Edition 4.1.1
Copyright (C) 2002-2005 RealVNC Ltd.
See http://www.realvnc.com for information on VNC.
Underlying X server release 70000000, The X.Org Foundation

Sat Sep 30 11:19:32 2006
vncext: VNC extension running!
vncext: Listening for VNC connections on port 5905
vncext: Listening for HTTP connections on port 5805
vncext: created VNC server for screen 0
Could not init font path element /usr/share/X11/fonts/OTF, removing from list!
Could not init font path element /usr/share/X11/fonts/CID/, removing from list!
/usr/bin/startxfce4: X server already running on display :5
Agent pid 4642

(xfce-mcs-manager:4661): libxfce4mcs-CRITICAL **: mcs_manager_add_channel_from_file: assertion `filename != NULL && strlen (filename) > 0' failed
Xlib: extension "RANDR" missing on display ":5.0".

** (xfce-mcs-manager:4661): CRITICAL **: find_master: assertion `mixer_handle != -1' failed

** (xfce-mcs-manager:4661): WARNING **: oss: No master volume
The program 'xfce4-panel' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadMatch (invalid parameter attributes)'.
(Details: serial 1246 error_code 8 request_code 72 minor_code 0)
(Note to programmers: normally, X errors are reported asynchronously;
that is, you will receive the error a while after causing it.
To debug your program, run it with the --sync command line
option to change this behavior. You can then get a meaningful
backtrace from your debugger if you break on the gdk_x_error() function.)

Sat Sep 30 11:20:03 2006
Connections: accepted: 127.0.0.1::36699
SConnection: Client needs protocol version 3.8
SConnection: Client requests security type VncAuth(2)

Sat Sep 30 11:20:06 2006
VNCSConnST: Server default pixel format depth 8 (8bpp) colour-map
VNCSConnST: Client pixel format depth 8 (8bpp) colour-map
X Error of failed request: BadWindow (invalid Window parameter)
Major opcode of failed request: 24 (X_ConvertSelection)
Resource id in failed request: 0x40000a
Serial number of failed request: 141
Current serial number in output stream: 141

(xfdesktop:4685): Gdk-WARNING **: GdkWindow 0x1200006 unexpectedly destroyed