On the starting Level I was able to navigate narrow corridors to get into the activated secret areas. I can't do this on the 2nd level. The only way to move diagonally is via the Mouse. The could be something blocking me that can't be seen because the corridor is too narrow, if this is the case then possible send an alert message such at "the way is blocked' of better yet "you are too fat to navigate this corridor"
I had the same problem on level 1. I was in the southwest corner of a room with a passage by my feet goimg west that I had just opened as a secret area. From my feet, the path went 2 squares left in a tight tunnel then turned south and ran for at least 3 squares south. A treasure was on the floor 2 squares from where the secret tunnel went south. I could not click to move to the square left of my feet, nor could I click the square beyond, nor any of the 3 squares south of that square. I keep mentioning my feet because of course there was some funky perspective stiff going on. I also tried clicking every square in the dark/blocked area beneath the clear part of the tunnel, no luck there either. I had to move on after a while.