Forced reinstall of application downloaded from Mac App Store

Context:
In Mac OSX Lion, I opened Launchboard and deleted an app that I had previously downloaded from the Mac App Store
Problem:
I was no longer able to download it, always getting the same annoying message from the Mac App Store software:
“A newer version of this app is already installed on this computer”

After spending hours trying to find the fix that does the trick (and, man, did I try them all: removed spotlight indexing from my HDD, removed launchpad db files, removed various folders and files), countless Trash emptied and reboots, I finally found the fix.

Here’s what worked for me (via stackexchange):
I opened up Terminal.app, pasted the line below, then pressed Enter:

A few minutes of waiting, and when it was done I launched the Mac App Store app and.. miracle: I was able to, once again, download my favorite app from the store.

I hope this will save a few hours for you as well