http://ubuntuforums.org/showthread.php?t=294771
I do not speak/ or maybe a word or two. a word in French. I think the next link
would help too.
forum.ubuntu-fr.org/viewtopic.php?pid=2302955

for trying to find a solution to my problem.
I already tried by myself what is explained at the first linked page
and now trying to install cf according second linked explanations
I'll let you know later

nothing of what I could try works.

I suppose either there is a configuration mismatching between Matacity
and Compiz
or my Xorg.conf has a bad instruction. I know its a very senitive file.
You can mistake
in "menu.lst" (Grub config) without very important consequence, instead
some error
in Xorg.conf may induce a screen stuck.
I go on seeking, may be replacing that file by olders.

Finally I've found (by myself, trying to make a new user session and
observing
how it behaves) THE solution. Maybe it can be useful for other people
who meet
some trouble with compiz volatil parameters. I added compiz-manager
(/usr/bin)
at starting applications and IT WORKS.

Anyway many thanks to all people who tried to help. If I have a solution for
a problem explained here, I'll give it.

your system might not run compiz well. It has trouble on many
systems.
Your graphics card might not be supported.
Did you check?

The trouble don't come for my graphics card indeed,
because the system has already worked fine.

I probably have mistaken a setting without being aware of it,
and the error came out after the xserver has reset.

I suppose something is mismatching between metacity and compiz.
Compiz is needed for the visual effects can work. But I tried to uninstall
all its components, then to rename the folders /home/myId/.compiz and
/home/myId/.config/compiz and after to re-install all the compiz components.
Nothing better, at each boot or session opening the visual effects have turn
to none (and till I don't change to normal, my windows decoration has
disappeared,
with the 3 buttons too - close , enlarge full screen, reduce to tray - )

Till now, nobody knows how compiz / metaciy work and how can one have
the parameters AUTOMATICALLY back at each session ?

Why does the sytem used to work properly till a time when at starting
the system, the visual effects DON'T WANT ANY MORE TO BE AUTOMATICALLY
kept ?

Does anyone know sufficiently Ubuntu for saying me how to have
visual effects automatically saved and recovered at every session ?

I'm certainly no expert but don't want you to think you are being ignored
here!

I have compiz on one system and it just works. It always comes back with the
same settings after every reboot. If you are having problems one thing you
might check is whether you have the right video card driver. That can make a
big difference if it is not the correct one and could cause going back to
the default or failsafe settings at every reboot.

There are some video cards that are very hard to work with in Linux and
there's not much one can do except find out the best choices and change your
hardware. Other than that I don't have any further ideas.

Hum the solution is probably independent from my video card
because the system has already worked well.
I must have made a wrong setting without being aware of it
and the result waited the reset of xserver to come out.

Anyway thank you for your nice words,
so I keep on being confident for a solution to appear.