I am upgrading from this: DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=14.10
DISTRIB_CODENAME=utopic
DISTRIB_DESCRIPTION="Ubuntu 14.10"
to
Ubuntu / Kubuntu 15.04

I can confirm I am getting this error during upgrade, many times:
...
Unpacking ksysguard (4:4.11.8-0ubuntu6) over (4:4.11.5-0ubuntu0.1) ...

(gtk-update-icon-cache-3.0:7760): GdkPixbuf-WARNING **: Cannot open pixbuf loader module file '/usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache': No such file or directory

This likely means that your installation is broken.
Try running the command
  gdk-pixbuf-query-loaders > /usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache
to make things work again for the time being.
Preparing to unpack .../libksignalplotter4_4%3a4.11.8-0ubuntu6_amd64.deb ...
Unpacking libksignalplotter4 (4:4.11.8-0ubuntu6) over (4:4.11.5-0ubuntu0.1) ...
,,,
Preparing to unpack .../humanity-icon-theme_0.6.5_all.deb ...
Unpacking humanity-icon-theme (0.6.5) over (0.6.4) ...

(gtk-update-icon-cache-3.0:27141): GdkPixbuf-WARNING **: Cannot open pixbuf loader module file '/usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache': No such file or directory

This likely means that your installation is broken.
Try running the command
  gdk-pixbuf-query-loaders > /usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache
to make things work again for the time being.

(gtk-update-icon-cache-3.0:27142): GdkPixbuf-WARNING **: Cannot open pixbuf loader module file '/usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache': No such file or directory

This likely means that your installation is broken.
Try running the command
  gdk-pixbuf-query-loaders > /usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache
to make things work again for the time being.
Preparing to unpack .../gir1.2-totem-plparser-1.0_3.10.2-0ubuntu1_amd64.deb ...
...
Processing triggers for hicolor-icon-theme (0.12-1ubuntu2) ...

(gtk-update-icon-cache:25668): GdkPixbuf-WARNING **: Cannot open pixbuf loader module file '/usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache': No such file or directory

This likely means that your installation is broken.
Try running the command
  gdk-pixbuf-query-loaders > /usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache
to make things work again for the time being.

(gtk-update-icon-cache-3.0:25669): GdkPixbuf-WARNING **: Cannot open pixbuf loader module file '/usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache': No such file or directory

This likely means that your installation is broken.
Try running the command
  gdk-pixbuf-query-loaders > /usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache
to make things work again for the time being.
dpkg: evolution-data-server-goa: dependency problems, but removing anyway as you requested:
 evolution-data-server depends on evolution-data-server-goa; however:
  Package evolution-data-server-goa is to be removed.

(Reading database ... 
...
Processing triggers for hicolor-icon-theme (0.12-1ubuntu2) ...

(gtk-update-icon-cache:17083): GdkPixbuf-WARNING **: Cannot open pixbuf loader module file '/usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache': No such file or directory

This likely means that your installation is broken.
Try running the command
  gdk-pixbuf-query-loaders > /usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache
to make things work again for the time being.

(gtk-update-icon-cache-3.0:17084): GdkPixbuf-WARNING **: Cannot open pixbuf loader module file '/usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache': No such file or directory

This likely means that your installation is broken.
Try running the command
  gdk-pixbuf-query-loaders > /usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders.cache
to make things work again for the time being.
Processing triggers for shared-mime-info (1.1-0ubuntu5) ...


It's literally everywhere.