The way to find out is to kill Lord Robert and, if the Cube fails to arrive, go to the Judge and click on the option "I lost it". If he replies "You never found it" or gives you something else, then the game has not set the Item Found flag, and using the edited-in Control Cube may not help. But there's no harm in trying. After all, if you've hit a game-killing problem, no extra harm can result from screwing the game up further.

I don't know whether this fault has arisen from editing or game corruption. However, if you want to restart it, you might consider uninstalling the game and re-installing it to make sure you have clean files on your drive.