The most recent versions of Commander no longer use the /l switch - there is a place in the Commander interface where you tell it which install of the game to launch. You can either type in the path or use the "Browse" button there to locate the desired .exe file.
Can't remember where exactly but should be somewhere in Commander's options screens.
I know this because the last time I reinstalled I also spent considerable time trying to make the /l switch work.
