Comment 17 for bug 197820

In my case, to make everything work, I had to add something to "applications startup" (I am not sure about the translation since I use a French system) OR in a terminal screen type "gnome-session-properties"

You can test this option with the command line interface to see if it works before addind it to the gnome-session-properties:

"compiz --replace"

This is, of course, a workaround, not the solution.