Description of problem:
gnome-shell does not start

Steps to Reproduce:
1a. gnome-shell --replace &
1b. (or) select gnome-shell as desktop effect
  
Actual results:
$ gnome-shell 
Avviso del window manager: Lo schermo 0 sul display «:0.0» ha già un window manager; provare a utilizzare l'opzione --replace per sostituirlo.
[frafra@rocketman ~]$ gnome-shell --replace
    JS ERROR: !!!   Exception was: Error: Requiring Shell, version none: Typelib file for namespace 'ClutterJson', version '1.0' not found
    JS ERROR: !!!     lineNumber = '0'
    JS ERROR: !!!     fileName = 'gjs_throw'
    JS ERROR: !!!     stack = 'Error("Requiring Shell, version none: Typelib file for namespace 'ClutterJson', version '1.0' not found")@:0
("Requiring Shell, version none: Typelib file for namespace 'ClutterJson', version '1.0' not found")@gjs_throw:0
@/usr/share/gnome-shell/js/ui/main.js:11
'
    JS ERROR: !!!     message = 'Requiring Shell, version none: Typelib file for namespace 'ClutterJson', version '1.0' not found'
    JS ERROR: !!!   Exception was: Error: Requiring Shell, version none: Typelib file for namespace 'ClutterJson', version '1.0' not found
    JS ERROR: !!!     lineNumber = '0'
    JS ERROR: !!!     fileName = 'gjs_throw'
    JS ERROR: !!!     stack = 'Error("Requiring Shell, version none: Typelib file for namespace 'ClutterJson', version '1.0' not found")@:0
("Requiring Shell, version none: Typelib file for namespace 'ClutterJson', version '1.0' not found")@gjs_throw:0
@/usr/share/gnome-shell/js/ui/main.js:11
Error("Chained exception")@:0
("Chained exception")@gjs_throw:0
@<main>:1
'
    JS ERROR: !!!     message = 'Requiring Shell, version none: Typelib file for namespace 'ClutterJson', version '1.0' not found'
Avviso del window manager: Log level 32: Execution of main.js threw exception: Error: Requiring Shell, version none: Typelib file for namespace 'ClutterJson', version '1.0' not found
[frafra@rocketman ~]$ Cannot register the panel shell: there is already one running.
Avviso del window manager: Received a _NET_WM_MOVERESIZE message for 0x4a00003 (Aggiungi/R); these messages lack timestamps and therefore suck.

Expected results:
Gnome shell should magically appear :D