Whenever I log into a desktop environment, it doesn't seem that compositing is starting. Unity 2D works fine, but when I go to Unity 3D Compiz doesn't start up. I have to type compiz --replace &
in terminal every time I login. Another example is when I log into a Cinnamon session, theming support is suddenly gone (although this may be a separate issue). If it helps im using the latest (295.40) NVIDIA drivers.
EDIT: I am having exactly the same issue in both cases, upgrading from 11.10 and with a clean installation, in 32 and 64 bits.
Many people seem to have the same problem.
You will need to delete the compiz and compiz-1 directories in your home .config directory.
Compiz files are then re-generated when you re-boot and log in again.
It worked for me.
sudoedit /usr/share/gnome-session/sessions/ubuntu.session
try to check if everything is ok there (it opens you session config file). There should be this line:
DefaultProvider-windowmanager=compiz
Also make sure that your computer is supporting everything 3D mode needs. For more info look here
The 'logical' answer would be to add
compiz --replace
to the startup programs. I had to answer for the people trying this that this not only didn't work for me, but it made unity not to start at all. I'm still looking for the answer as I need compiz working perfectly fine on startup.