I'm assuming you're running around in the dark by yourself at this point in the game. Normally you just go north from room 12 to get into room 11. But if you have already been in that room when you were walking around with Ford it's not going to let you in again. If you remember getting the firecrackers item then you were already in there.
If you have already made it into room 11 before, when you run into the wall the player should say something like "There used to be a room here! I know there was!"
...if not then I coded something wrong.