After have done :

sudo aptitude update
sudo aptitude dist-upgrade

the global menu is broken (i.e., I don't have global menu, instead the menu is shown on application windows). Moreover, when I right click on the desktop and select "Change Desktop Background", instead of "Appearance" settings, I get "System Settings" window (from which I can of course get to the appearance settings by clicking "Appearance").

Could anynone help me?

Thanks in advance