Front Row doesn't work when I'm on dual screen

Hi everyone, I have a very annoying problem with my MacBook unibody probably since the last Front Row update.

After several hours my mac is running linked to my LCD screen through MiniDisplay Port - VGA connector, Front Row simply doesn't start. It fades to black for a while but then it immediately fades back to the desktop. I uninstalled every application might have affected Front Row (Caffeine, LastFm, TV Row) but it was useless. I even tried to fix permissions in the Disk Utility, but it didn't help.

I also noted that in the same circumstances Exposé and Dashboard don't work if I press the F3 and F4 keys respectively on the keyboard, but if I click on their icons (or, in the case of Dashboard, if I do the 4-finger gesture on the trackpad) they run normally.

Anyway, when my MacBook isn't plugged with the LCD screen, Exposé, Front Row and Dashboard work fine.

Can you help me? Thanks in advance.