If your graphics are broken you can fix with the new ddraw version.** Read how to install it here **
I've mentioned it before in a different thread but I've had free castle games with TONS of dead spots and defiantly were not caused by walls.
If you can't replicate the dead square phenomenon, it's doubtful you fully understand it. Would it be possible tofarm in an entire expansion like 4 with dead squares??? =O