It seems to be a Path issue: I have found "org.virt-manager.virt-manager.gschema.xml" inside /usr/local/share/glib-2.0/schemas"; 
I suppose they are searched inside "/usr/share/glib-2.0/schemas". 
There must a link with the bug in 6. in previous comment.

Same bug here:
https://www.redhat.com/archives/virt-tools-list/2013-July/msg00056.html

Yes, as mentioned in my mail in that thread, there's two issues:

- python setup.py install isn't running glib-compile-schemas where it is
dumping our schema.
- gsettings likely doesn't know to look in /usr/local/share for schemas.

I don't want to go down the route of making this automatically work, since virt-manager would have to mess with GSETTINGS_SCHEMA_DIR. However we can at least make the build system warn about what manual steps are likely required.

Could you elaborate on the manual intervention required for gsettings?

As I said before, I thing there's an issue with the global path setting somewhere: /usr/share is used instead of /usr/local/share. Here's why:

I've compiled the schemas with: 
root@VBox-Ubuntu-14:/usr/local/share/glib-2.0/schemas# glib-compile-schemas /usr/local/share/glib-2.0/schemas

The "gschemas.compiled" has been coorectly created in the same directory. Please note that this file looks identical to the "virt-manager-1.0.1/data/gschemas.compiled"
Then:

virt-manager-1.0.1/# export GSETTINGS_SCHEMA_DIR=/usr/local/share/glib-2.0/schemas

Then:
 
virt-manager-1.0.1/# virt-manager --debug[sam., 26 juil. 2014 14:53:41 virt-manager 17818] DEBUG (cli:187) Launched with command line: /usr/local/share/virt-manager/virt-manager --debug
[sam., 26 juil. 2014 14:53:41 virt-manager 17818] DEBUG (virt-manager:150) virt-manager version: 1.0.1
[sam., 26 juil. 2014 14:53:41 virt-manager 17818] DEBUG (virt-manager:151) virtManager import: <module 'virtManager' from '/usr/local/share/virt-manager/virtManager/__init__.pyc'>
[sam., 26 juil. 2014 14:53:41 virt-manager 17818] DEBUG (virt-manager:209) GTK version: 3.10.8
[sam., 26 juil. 2014 14:53:41 virt-manager 17818] DEBUG (engine:484) libguestfs inspection support: False
[sam., 26 juil. 2014 14:53:41 virt-manager 17818] DEBUG (systray:152) Showing systray: False
[sam., 26 juil. 2014 14:53:41 virt-manager 17818] DEBUG (cli:182) Uncaught exception:
Traceback (most recent call last):
  File "/usr/local/share/virt-manager/virtManager/engine.py", line 132, in _activate
    self.show_manager()
  File "/usr/local/share/virt-manager/virtManager/engine.py", line 924, in show_manager
    self._do_show_manager(None)
  File "/usr/local/share/virt-manager/virtManager/engine.py", line 868, in _do_show_manager
    manager = self.get_manager()
  File "/usr/local/share/virt-manager/virtManager/engine.py", line 829, in get_manager
    obj = vmmManager()
  File "/usr/local/share/virt-manager/virtManager/manager.py", line 117, in __init__
    vmmGObjectUI.__init__(self, "manager.ui", "vmm-manager")
  File "/usr/local/share/virt-manager/virtManager/baseclass.py", line 203, in __init__
    self.builder.add_from_string(file(uifile).read())
IOError: [Errno 2] No such file or directory: '/usr/share/virt-manager/ui/manager.ui'

Traceback (most recent call last):
  File "/usr/local/share/virt-manager/virtManager/engine.py", line 132, in _activate
    self.show_manager()
  File "/usr/local/share/virt-manager/virtManager/engine.py", line 924, in show_manager
    self._do_show_manager(None)
  File "/usr/local/share/virt-manager/virtManager/engine.py", line 868, in _do_show_manager
    manager = self.get_manager()
  File "/usr/local/share/virt-manager/virtManager/engine.py", line 829, in get_manager
    obj = vmmManager()
  File "/usr/local/share/virt-manager/virtManager/manager.py", line 117, in __init__
    vmmGObjectUI.__init__(self, "manager.ui", "vmm-manager")
  File "/usr/local/share/virt-manager/virtManager/baseclass.py", line 203, in __init__
    self.builder.add_from_string(file(uifile).read())
IOError: [Errno 2] No such file or directory: '/usr/share/virt-manager/ui/manager.ui'


Have you noticed the "No such file or directory: '/usr/share/virt-manager/ui/manager.ui'" errors? 
This file exists in the folder... /usr/local/share/virt-manager/ui/

The manual intervention I meant was glib-schemas-compile and usage of GSETTINGS_SCHEMA_DIR to point to /usr/local

The UI path issue I haven't seen specifically, perhaps we are hardcoding /usr/share somewhere, instead of using whatever the configured prefix is.

FWIW, I think it would be worth setting GSETTINGS_SCHEMA_DIR automatically in virt-manager. I had this same problem with Entangle and even though I clearly tell people what to do in summary printed by configure, there was still a never ending stream of bug reports. The code to set it isn't that difficult


https://gitorious.org/entangle/entangle/source/939ff0f16ee568287221da47376a679f147cb8cc:src/backend/entangle-preferences.c#L793

@ Daniel Berrange: I have already tried to set GSETTINGS_SCHEMA_DIR. Other symptoms have been exposed afterwards which seem to indicate that there's a core issue with some basic path somewhere. 

It seems that some parts of the code use /usr/share while some other parts use /usr/local/share.

For example, when we install virt-manager with "python setup.py install",
- virt-manager tree is installed under /usr/local/share
- but all virt-* scripts inside /usr/local/bin point to usr/share/virt-manager/
- and /usr/share/glib-2.0/schemas/gschemas.compiled has been modified: maybe virt-manager-1.0.1/data/gschemas.compiled has been merged into it
- and there are attempts to read /usr/share/virt-manager/ui/manager.ui instead of /usr/local/share/virt-manager/ui/manager.ui

I added a warning pointing at GSETTINGS_SCHEMA_DIR to setup.py install if not installing into /usr/share