Compiz Instead Metacity When Starting Gnome

Suddenly Metacity was being loaded in lieu of Compiz when starting Gnome. I tried restart compiz with:

compiz --replace

but it did not work and Metacity kept itself up and running.

What worked for me was open gconf-editor (Alt+F2 > “gconf-editor” > Enter) and navigate trough “desktop > gnome > session > required_components and set windowmanager key as “compiz”. The next time you start Gnome, Compiz will be loaded.