macnbc: I've heard of this issue before (a friend of mine ran into it playing the original game way back when) but am not quite sure how to fix it. (The boulder should crash through the wall after about 5-10 seconds.)
Obviously the first thing I can think of would be to jump to another time zone and jump back to see if that somehow "resets" it. Saving the game just BEFORE the suspect wall and reloading might help as well.
Hope that helps. Good luck!
EDIT: I found another site referencing this bug that offered the following:
"I've heard two solutions to fixing it: 1) restore from a location inside the castle or at least at some place other than where you wait for the catapult (you can use the fast movement option to get back to the catapult quickly) or 2) turn around 360 degrees at that same spot."
hey, i have this glitch, and absolutely nothing less than restarting the game will fix it. sometimes that won't matter if the glitch happens again.
unfortunately for me, i didn't know it was a glitch, and i completed like half of the game, including that nerve-racking part in the space ship, before i realized that i would have to start over to complete the game.
so i started over, but there is no guarantee that it won't happen again one of the times i have to go back to the castle, which is two or three times.
i guess i've been pretty lucky with game breaking bugs that other folks seem to encounter, so i shouldn't be too peeved, but i am certainly hating this game right now.
WORD TO THE WISE, visit the castle later in the game, and SAVE before you go there, just in case this bug happens to you.