WARNING: gtk-update-icon-cache-3.0: The generated cache was invalid.

Also occurs for me with version 0.0.26.

Because of this the monochrome icons are not available, standard gnome icons are used instead.

I believe the underlying problem is Bug #741899, that SVG images are not recognized.

At cypermox's suggestion, tried building without scour:

  $ sudo dpkg -i ../ubuntu-mono_0.0.26-noscour_all.deb
  gtk-update-icon-cache-3.0: The generated cache was invalid.
  WARNING: icon cache generation failed for /usr/share/icons/ubuntu-mono-light
  x4

unfortunately no difference.

For reference: (paraphrased): bzr branch lp:ubuntu-mono && cd ubuntu-mono && sed -p -i -e 's/ --with-scour//' debian/rules && debuild -b && dpkg -i ../*.deb

  open("/usr/share/icons/ubuntu-mono-light/.icon-theme.cache", O_RDONLY|O_LARGEFILE) = 3
  fstat64(3, {st_mode=S_IFREG|0644, st_size=40652, ...}) = 0
  mmap2(NULL, 40652, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7785000
  close(3) = 0
  munmap(0xb7785000, 40652) = 0

  write(2, "gtk-update-icon-cache-3.0", 25) = 25
  write(2, ": ", 2) = 2
  write(2, "The generated cache was invalid."..., 33) = 33
  exit_group(1) = ?

Post-clean install:

  ls -1 /usr/share/icons/{LoginIcons,ubuntu-mono-dark,ubuntu-mono-light}/{.,}icon-theme.cache
  ls: cannot access /usr/share/icons/LoginIcons/.icon-theme.cache: No such file or directory
  ls: cannot access /usr/share/icons/ubuntu-mono-dark/icon-theme.cache: No such file or directory
  ls: cannot access /usr/share/icons/ubuntu-mono-light/icon-theme.cache: No such file or directory
  /usr/share/icons/LoginIcons/icon-theme.cache
  /usr/share/icons/ubuntu-mono-dark/.icon-theme.cache
  /usr/share/icons/ubuntu-mono-light/.icon-theme.cache

so whatever it is, is occuring only during processing of the ubuntu-mono-{dark,light} subdirectories, and then sum of the icons in '/LoginIcons' aren't a contributing factor to the failure.

Removing "--quiet" from the shell script:

  /usr/sbin/update-icon-caches

produces the interesting juxtaposition:

  gtk-update-icon-cache-3.0: The generated cache was invalid.
  gtk-update-icon-cache-3.0: Cache file created successfully.

the executable itself is in:

  libgtk-3-bin: /usr/bin/gtk-update-icon-cache-3.0

  gtk/updateiconcache.c:1531

    if (!validate_file (tmp_cache_path))
    {
      g_printerr (_("The generated cache was invalid.\n"));
      /*g_unlink (tmp_cache_path);*/
      exit (1);
    }

   …

  gtk/updateiconcache.c:1398
  validate_file (const gchar *file)
  {
  …
    if (!_gtk_icon_cache_validate (&info))
    {

  gtk/gtkiconcachevalidator.c:371

    371 /**
    372 * _gtk_icon_cache_validate:
    373 * @info: a CacheInfo structure
    374 *
    375 * Validates the icon cache passed in the @cache and
    376 * @cache_size fields of the @info structure. The
    377 * validator checks that offsets specified in the
    378 * cache do not point outside the mapped area, that
    379 * strings look reasonable, and that pixbufs can
    380 * be deserialized. The amount of validation can
    381 * be controlled with the @flags field.
    382 *
    383 * Return value: %TRUE if the cache is valid
    384 */
    385 gboolean
    386 _gtk_icon_cache_validate (CacheInfo *info)

  /**
   * _gtk_icon_cache_validate:
   * @info: a CacheInfo structure
   *
   * Validates the icon cache passed in the @cache and
   * @cache_size fields of the @info structure. The
   * validator checks that offsets specified in the
   * cache do not point outside the mapped area, that
   * strings look reasonable, and that pixbufs can
   * be deserialized. The amount of validation can
   * be controlled with the @flags field.
   *
   * Return value: %TRUE if the cache is valid
   */
  gboolean
  _gtk_icon_cache_validate (CacheInfo *info)
  {

nb. it could also be interaction with:

  debian/patches/060_ignore-random-icons.patch

I just tried to rebuild gtk without that patch, but the cache generation still fails to validate.

Not an issue in GTK+ at all. In a brief moment of lucidity, I tried to generate icon caches for each of the subdirectories:

sudo find . -type d -print -exec gtk-update-icon-cache -ft /usr/share/icons/ubuntu-mono-dark

Only the animation directory fails. Turns out there are duplicate symlinks for the nm-stage02-connecting03 icon.

Wooo!

  Setting up ubuntu-mono (0.0.27) ...
  gtk-update-icon-cache-3.0: Cache file created successfully.
  gtk-update-icon-cache-3.0: Cache file created successfully.
  gtk-update-icon-cache-3.0: Cache file created successfully.

1) this package misses an explicit Build-Depends on python-rsvg
2) dh_scour fails on several files, because cmpsvg dies at random.
3) the package indeed installs cleanly, this time. Hurray! :-)
4) it however still doesn't fix the broken icon issue in notification-area or in GDM.

This bug was fixed in the package ubuntu-mono - 0.0.27

---------------
ubuntu-mono (0.0.27) natty; urgency=low

  * Clean up stray duplicate symlinks for the nm-stage02-connecting03 icon
    under animations/ that would make icon cache validation fail. (LP: #741387)
 -- Mathieu Trudel-Lapierre <email address hidden> Wed, 30 Mar 2011 16:14:45 -0400

Well I believe this issue (broken notification area) is not fixed.
I still do not have Nm-applet icon in notification area.
And still, downgrading to the previous libappindicator1_0.2.99-0ubuntu1 solves the issue.

The broken notification area (or icons in it) is reported in the bug #741385
That is marked as duplicate to this bug report.

ubuntu-mono updated to 0.0.27, but same problem exists

bug #741385 is not marked anymore as being a duplicate of this one,
So please comment on bug #741385 if your icons in the notification area are still broken.