Created attachment 14317 [details]
screenshot of broken volume control icon

I used the official gnome tarbals.

Are you talking about the icon with the little red "x" in the upper
right panel? Is this the volume control applet?

the icon with the little red "x" in the upper right panel is indeed
the volume control applet where I'm talking about.

the icon with the little red "x" in the upper right panel is indeed
the volume control applet where I'm talking about.

In the directory {prefix}/share/pixmaps/mixer there should be a bunch
of png files - 

volume-medium.png  volume-mute.png
volume-max.png     volume-min.png     volume-zero.png

Are they there?

Yes, they're there...

compukid@pc1:/usr/local/share/pixmaps/mixer$ ls -lh
total 24K
-rw-r--r--    1 root     staff        1.6K Feb 12 18:45
gnome-mixer-applet.png
-rw-r--r--    1 root     staff        2.4K Feb 12 18:45 volume-max.png
-rw-r--r--    1 root     staff        2.1K Feb 12 18:45 volume-medium.png
-rw-r--r--    1 root     staff        1.9K Feb 12 18:45 volume-min.png
-rw-r--r--    1 root     staff         972 Feb 12 18:45 volume-mute.png
-rw-r--r--    1 root     staff        1.6K Feb 12 18:45 volume-zero.png

hmm... where is the rest of gnome installed? The applet may be looking
in /usr/share/pixmaps/mixer not /usr/local/share/pixmaps/mixer

gnome is installed in the default (/usr/local) location.
I'll try to make some symlinks so the png's will be available in both
locations.

which keys in gconf are used for settings of the image of the
volume-control icon?

There are no gconf keys controlling the images. As John said, the
applet looks in {prefix}/share/pixmaps/mixer for the icons. 

Do you have an older version of GNOME installed elsewhere? It may be
the applet is looking in a directory of a different GNOME installation.

Here's how you should be able to find where mixer is looking: 
1) remove the mixer applet from the panel
2) run 'strace -eopen /usr/local/libexec/mixer-applet-2' (or wherever
the binary is located)
3) add the mixer applet to the panel using the right click menu

Now watch for output where it tries to open the image files. Note what
directory it is looking in.

Created attachment 14614 [details]
output of "strace -eopen /usr/local/libexec/mixer_applet2"

Seems like he's searching for the file: 'NULL'

(mixer_applet2:15481): Gtk-WARNING **: Useless GtkIconSource contains
NULL filename and pixbuf
                                                                     
          
(mixer_applet2:15481): Gtk-CRITICAL **: file gtkiconfactory.c: line
2091 (gtk_icon_source_set_filename): assertion `filename == NULL ||
g_path_is_absolute (filename)' failed

Actually, the problem is that it prepends the wrong prefix to icon path:
open("NONE/share/pixmaps/mixer/gnome-mixer-applet.png", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/local/lib/charset.alias", O_RDONLY|O_LARGEFILE) = -1 ENOENT (No such file or directory)

This is where the icon is opened:
mixer.c:841:    gnome_window_icon_set_from_file (GTK_WINDOW (about), GNOME_ICONDIR"/mixer/gnome-mixer-applet.png");

and this is what the definition of the GNOME_ICONDIR in config.h is:
#define GNOME_ICONDIR "NONE/share/pixmaps"

It appears that the problem is the configure script?

Changing the config.h manually and recompiling the applets fixed the problem for me

Yeah that's correct. Somehow GNOME_ICONDIR should be set to
"/something/share/pixmaps". I'm not sure why it's not be set correctly.

Here's the relavant line 253 from configure.in:
AC_DEFINE_UNQUOTED(GNOME_ICONDIR, "${prefix}/share/pixmaps")

For you guys ${prefix} should be /usr/local, but for some reason it is
substituting NONE.

The code hasn't changed in years for this. What version of automake,
autoconf are you using?

compukid@pc1:~$ automake --version
automake (GNU automake) 1.4-p6
 
Copyright (C) 1999, 2001 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE.
 
Written by Tom Tromey <tromey@redhat.com>
compukid@pc1:~$ autoconf --version
Autoconf version 2.13

I also found this line in config.h
#define PREFIX "NONE"

"./configure --prefix=/usr/local" did fix it for me...

*** This bug has been marked as a duplicate of 104935 ***